V.aTr.ut  Aphides  In  California 


By 
.M.  Davidson 


/    •    ' 


UNIVERSITY  OF  CALIFORNIA 
AT    LOS  ANGELES 


BULLETIN    OF   THE 


No.  100 


SB 


Contribution  from  the  Bureau  of  Entomology,  L.  O.  Howard,  Chief. 
August  31,  1914. 

(PROFESSIONAL  PAPER.) 


WALNUT  APHIDES  IN  CALIFORNIA. 

By  W.  M.  DAVIDSON, 

Scientific  Assistant,  Deciduous  Fruit  Insect  Investigations. 

INTRODUCTION. 

The  study  of  walnut  aphides  dealt  with  in  the  following  pages  was 
in  early  hi  the  year  1911  and  continued  until  the  summer  of  1913. 

ie  observations  were  at  first  made  at  San  Jose,  CaL,  but  after  Sep- 
iber,  1912,  the  work  was  done  chiefly  at  Walnut  Creek,  Cal.  Prac- 

5 ally  all   the  life-history  observations  were  made  at   the  former 

jality,  and  much  of  the  control  work  was  done  at  Walnut  Creek. 

ie  habits  of  the  aphides  do  not  vary  materially  throughout  Cali- 
Drnia.  It  was  at  first  the  writer's  intention  to  confine  his  studies  to 
ie  European  walnut  aphis  (OhromapJiis  juglandicola  Kalt.),  as  this 
>ecies  alone  infests  walnuts  of  commercial  value  grown  in  California, 

it  latterly  two  native  species  of  Aphididae  were  found  to  be  pests 

.  native  walnuts  much  used  for  stock  on  which  to  graft  the  European 

Persian  nut,  and  thus  the  studies  were  extended  so  as  to  include 

three  species.    The  two  native  aphides  above  mentioned  are  Monellia 

iryse  Monell,  .the  American  walnut  aphis,  which  affects  the  eastern 

lack  walnut  (Juglans  nigra)  and  Monellia  caryella  Fitch,  the  little 

ikory  aphis,1  which  affects  the  California  black  walnut  (Juglans 

\ilifornica).     Both  of  these  species  infest  the  Royal  Hybrid  walnut 

cross  between  the  eastern  black  walnut  and  the  California  black 

^alnut),  while  the  Paradox  Hybrid  walnut   (a  cross  between  the 

European  walnut  and  the  California  black  walnut)  is  attacked  by  the 

European  walnut  aphis  and  to  a  lesser  extent  by  the  little  hickory 

)his.     Both  of  these  hybrids  are  rapid  growers,  and  a  certain  per- 

jntage  of  the  seedlings  obtained  from  the  crossings  makes  good 

>ck  on  which  to  graft  the  commercial  varieties  of  nuts.  The  great 
tajority  of  European  nuts  and  their  varieties  are  grown  in  California 

I1  This  is  the  name  Fitch  gave  to  species  which  he  found  on  hickory,  and  it  seems  best  to  retain  it, 
[though  rather  an  unfortunate  title  in  so  far  as  California  is  concerned,  as  the  only  wild  member  of  the 
adace®  in  that  State  is  Juglans  californica. 

40859°— Bull.  100—14 1 


BULLETIN   100,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

on  roots  of  either  the  California  black  walnut  straight  or  on  roots  of 
one  or  the  other  of  these  two  hybrids.  When  a  graft  has  been  made 
and  both  stock  and  scion  are  putting  out  leaves  simultaneously,  more 
I  than  one  species  of  aphis  will  usually  occur  on  the  same  tree.  In 
such  a  case  the  two  species  feed  on  their  own  particular  host,  but  the 
migrant  forms  of  either  may  bo  found  resting  on  foliage  of  the  oppo- 
site host.  The  Paradox  and  Royal  hybrids  are  used  in  various  parts 
of  California  as  shade  trees  and  will  furnish  a  fine  grade  of  wood, 
which  will  take  on  a  high  polish. 

THE  EUROPEAN  WALNUT  APHIS  (Chromaphis  juglandicola  Kaltenbach). 

Lachnus  juglandicola  Kaltenbach,  Monographie  der  Familien  der  Pflanzenlause, 

Aachen,  1843. 
Callipterus  juglandicola  Koch,  Die  Pflanzenlause  Aphiden,  Nurnberg,  p.  224, 

1857. 

Callipteras  juglandicola  Passerini,  Gli  Afidi,  Parma,  1860. 
Callipterus  juglandis  Walker,  The  Zoologist,  ser.  2,  v.  5,  p.  2000,  Feb.,  1870. 
Pterocallis  juglandicola  Buckton,  Monograph  of  the  British  Aphides,  v.  3,  London, 

1881,  p.  32-34. 

Callipterus  juglandicola  Schouteden,  Mem.  Soc.  Ent.  Belg.,  v.  12,  p.  209-210. 
Chromaphis  juglandicola  Essig,  Mo.  Bui.  Cal.  State  Com.  Hort.,  v.  1,  no.  5,  p. 

190-194,  figs.  72-73,  April,  1912. 

In  1870  Walker  erected  the  genus  ChromapJiis  and  designated 
Callipterus  juglandicola  Kaltenbach  as  the  type  species.  Reference 
to  this  is  made  by  H.  F.  Wilson  in  his  paper  "A  Key  to  the  Genera 
and  Notes  on  the  Synonymy  of  the  Tribe  Callipterini,  Family  Aphi- 
didae,"  Canad.  Ent.,  v.  42,  no.  8,  p.  253-259,  Aug.,  1910. 

HISTORY  OF  THE  SPECIES. 

The  species  was  described  originally  by  J.  H.  Kaltenbach  in  his 
"Monographie  der  Familien  der  Pflanzenlause"  as  Lachnus  juglandi- 
cola. A  somewhat  free  translation  of  this  description  is  as  follows : 

Wingless:  Pale  yellow,  egg-shaped,  flat,  square,  incised,  and  armed  with  glandular 
hairs  on  the  margins;  legs  whitish- yellow,  a  black  spot  on  the  apex  of  the  hind  femora. 
Length,  \" '. 

Winged:  Yellow;  eyes  red;  antenna)  whitish,  with  black  rings;  cornicles  yellow, 
hardly  noticeable;  tail  lacking. 

This  tree  louse  occurs  sporadically  in  June  and  July  in  numbers  under  the  leaves 
of  the  walnut  tree  (Juglans  regia). 

Wingless:  Antenna;  shorter  than  the  head  and  thorax  combined,  not  markedly 
jointed,  whitish-yellow.  Apex  of  antennae  black,  of  third  joint  ringed  black.  Eyes 
light  red;  beak  short,  scarcely  reaching  to  the  first  coxae.  On  the  dorsum  occur  two 
longitudinal  rows  of  black  spots,  which  are  absent  on  younger  individuals.  Cornicles 
and  tail  lacking.  Legs  hyaline  whitish-yellow;  a  black  spot  is  found  on  the  upper 
side  of  the  hind  femora  at  their  apices. 

Winged:  Antennae  noticeably  shorter  than  the  body,  pale,  the  four  major  joints 
black  at  their  apices;  third  joint  distally  enlarged;  sixth  joint  with  a  gradually 
tapering  thin  apex.  The  body  is  yellow;  in  many  cases  the  black  dorsal  spots  of  the 
abdomen  are  absent;  .in  other  cases  but  two^to  six  are  present;  cornicles  scarcely  per- 


WALNUT  APHIDES  IN   CALIFORNIA.  3 

ceptible,  yellow;  tail  not  present.  Legs  pale;  the  spots  on  the  apex  of  the  hind 
femora  are  larger  than  those  of  the  wingless.  In  well-colored  examples  such  spots 
occur  on  the  middle  femora  and  those  on  the  hind  femora  are  enlarged  into  a  ring. 
The  wings  are  transparent;  the  stigma  yellow,  cubitus  and  the  two  inner  veins  brown 
and  markedly  stouter  at  the  base,  then  gradually  becoming  finer  and  paler;  veins  of 
lower  wing  and  wing  margin  pale  yellow;  stigmatic  or  fourth  vein  very  fine  and 
strongly  curved. 

There  is  no  doubt   that  Kaltenbach's  species  is  the  same  that 

occurs  commonly  all  over  California  on  the  European  walnut.     The 

v^  black  femoral  spot,  together  with  the  antennse  as  described,  estab- 

\.^  lishes  its  identity.     Kaltenbach's  wingless  form  appears  to  be  the 

oviparous  female  in  her  penultimate  molt,  for  the  true  apterous  vivip- 

s^arous  female — a  common  form  in  the  majority  of  plant  lice — does 

Qft  not  exist,  or,  if  it  does,  is  extremely  rare,  the  author  in  two  years  of 

close  observation  having  failed   to   observe   it.     Buckton    (1872) 1 

i  gives  a  description  of  the  apterous  viviparous  form,  but  he  also  seems 

(  v'to  have  had  before  him  the  immature  oviparous  form. 

The  bisect  probably  occurs  wherever  the  European  walnut  is 
grown.  It  has  been  reported  from  all  over  Europe,  as  well  as  from 
the  States  of  Colorado  (Gillette,  1910),  Oregon  (Wilson  and  Lovett, 
1911-12),  and  California  (Essig,  1909). 

GENERAL  DESCRIPTION;  CHARACTER  AND  EXTENT  OF  INJURY. 

This  aphidid  is  a  small,  lemon-yellow  insect,  about  one-sixteenth 

~^of  an  inch  in  length.     It  occurs  sporadically  on  the  underside  of  the 

leaves  and  on  the  young  fruit  of  the  European  walnut  (Juglans  regia) 

and  its  cultivated  forms  and  hybrids.     It  appears  on  the  upper  sur- 

\face  of  the  leaf  only  at  times  of  very  severe  infestation.     It  is  to  be 

"'found  from  late  February  or  early  March  until  December,  persisting 

xas  long  as  the  leaves  remain  on  the  tree,  but  is  present  in  greatest 

^numbers  during  the  months  of  July  and  August.     As  many  as  200 

\  individuals  may  occur  on  a  single  large  leaflet  if  infestation  be  severe, 

o^  while  the  author  has  observed  over  30  aphides  on  a  single  young  nut. 

Nuts  badly  infested  while  young  never  attain  their  normal  size. 

Many  of  them  mature  half-sized,  covered  on  the  upper  surface  with 

the  black  sooty  fungus  which  thrives  on  the  sticky  exudations  of  the 

aphides.     Attacks  on  the  tree  year  by  year  also  materially  reduce 

its  vitality,  since  the  aphides  will  be  present  in  the  spring  even  before 

the  leaves  have  opened  and  will  remain  until  these  drop. 

Plate  I,  figure  1,  shows  the  difference  in  size  between  infested  and 
uninfested  nuts  of  one  variety  of  European  walnut,  while  Plate  I, 
figure  2,  demonstrates  the  appearance  of  the  sooty  fungus  on  a 
walnut  leaf. 

i  Dates  in  parentheses  refer  to  the  Bibliography,  p.  47. 

242747 


BULLETIN  100,   U.   S.   DEPARTMENT  OF  AGEICULTURE. 


LIFE  HISTORY  AND  TECHNICAL  DESCRIPTIONS. 

THE  VIVIPAROUS  OR  ASEXUAL  FORMS. 

When  the  young  stem-mother  is  ready  to  emerge  in  the  spring  she 
causes  the  shell  of  the  winter  egg  to  burst  with  a  longitudinal  slit  on 
the  dorsal  surface  from  the  micropylar  end.  (See  fig.  1.)  Egress  is 
performed  head  first,  and  antennae  and  legs  are  requisitioned  by  the 
young  larva  in  worming  its  way  out  of  the  shell.  While  the  process 
of  emerging,  which  occupies  half  an  hour  or  more,  is  taking  place,  the 
aphis  assumes  an  erect  position  at  right  angles  to  the  long  axis  of  the 
egg.  After  the  exit  of  the  young  the  eggshell  has  a  large  triangular 
hole  at  the  micropylar  end. 

As  soon  as  the  buds  begin  to  swell  in  early  spring  these  stem-mothers 
hatch  and  continue  hatching  until  the  leaves  have  fully  opened  out,  at 
which  time  all  will  have  issued  from  the  egg.  The  earliest  plant-lice 
to  emerge  may  be  seen  wandering  over  the  bare  twigs  and  buds, 
apparently  feeding  a  little  upon  the  scales  protecting  the  unopened 
buds,  but  not  showing  much  growth  until  the  buds 
have  opened  and  can  afford  nourishment. 

Undoubtedly  many  of  the  aphides  that  hatch 
early  die  of  ill  nourishment,  and  some  of  these  do 
not  attain  their  full  development  for  six  or  seven 
weeks,  while  those  hatching  later  and  finding 
tender  food  in  abundance  become  full  grown  at 
the  end  of  five  weeks-  Certain  it  is  that  on  a 
times  natural  size.  (Origi-  particular  tree  the  stem-mothers  all  became 
winged  almost  simultaneously.  On  trees  which 
leaf  early  the  stem-mothers  will  begin  emerging  [from  the  egg  as 
early  as  February  15,  but  on  the  Franquette  and  such  late  varie- 
ties no  aphides  will  be  found  until  in  April.  Immediately  after 
hatching  the  lice  seek  the  buds-or  young  leaves.  In  the  former  case 
the  aphides  crawl  in  between  the  scales,  but  on  the  leaves  they 
appear  on  the  lower  or  exposed  side,  notwithstanding  the  fact  that 
much  better  protection  is  afforded  by  the  upper,  as  yet  unfolded,  sur- 
face which  at  that  time  is  almost  entirely  hidden  from  view.  Possibly 
the  sticky  character  of  the  upper  surface  of  the  leaves  repels  them. 
Table  I  indicates  the  life  cycle  of  four  stem-mothers  which  hatched 
after  the  buds  had  opened. 

TABLE  1.— Period  of  development  of  the  stem-mother  of  Chromaphis  juglandicola,  San 
Jose,  Cal.,  1912. 


No.  of  individual. 

Date  of 
hatching. 

Date  of 
acquiring 
wings. 

Period  from 
hatching  to 
maturity. 

1.... 

Mar.  24 

Apr.  28 

Day, 

2  
3 

24 

24 

28 

28 

35 
35 

4  

24 

29 

36 

Average  period. 

35.25 

Bui.  100,  U.  S.  Dept.  of  Agriculture. 


PLATE  I. 


FIG.  1.— THREE  MATURED  NUTS  OF  EUROPEAN  WALNUT  SEEDLING. 

[Middle  nut  natural  size,  other  two  undersized  from  attack  by  aphides.] 


FIG.  2.— UPPER  SIDE  OF  THREE  LEAFLETS  OF  EUROPEAN  WALNUT  SEEDLING. 

[The  central  leaflet  shows  growth  of  fungus  thriving  upon  the  exudation  of  aphides  above. 
Two-thirds  natural  size.] 


WALNUT  APHIDES  IN   CALIFORNIA.  5 

THE  STEM-MOTHER;  NEWLY  HATCHED  YOUNG  (FIG.  2). 

Oval,  lemon  yellow.  Eyes  red,  of  moderate  size.  Antennae  3-jointed,  not  quite 
reaching  to  base  of  second  coxae;  joint  III  nearly  three  times  as  long  as  joints  I  and  II 
together.  Legs  comparatively  long,  entirely  pale.  Body  covered  with  capitate 
hairs.  Cornicles  very  small,  pale  whitish-yellow,  hardly  raised  above  the  surface  of 
the  body.  Cauda  small,  pale,  bluntly  conical.  Beak  entirely  pale,  reaching  second 
coxae.  Black  knee  spots  characteristic  of  this  species  absent.  Measurements :  Length 
of  body,  0.72  mm.;  width,  0.30  mm.;  antenna,  joint  I,  0.04  mm.;  joint  II,  0.035  mm.; 
joint  III,  0.145  mm.  Almost  immediately  after  birth  the  legs  and  antennae  turn 
dusky  gray  and  the  dark  abdominal  spots  appear.  In 
this  respect  the  young  of  the  stem-mothers  differ  from 
those  of  all  other  generations,  for  the  appendages  of  the 
young  aphides  of  subsequent  broods  never  turn  entirely 
dusky  nor  do  the  abdominal  spots  appear  so  early. 

THE  STEM-MOTHER;  4  DAYS  OLD. 

Yellowish-green,  flatly  oval,  closely  appressed  to  the 
surface  of  the  leaflet  or  bud  scale.  Antennae  and  legs 
dusky  gray.  Eyes  circular,  red,  small.  Head,  thorax, 
two  proximal  antennal  joints,  and  abdomen  bearing  capi- 
tate hairs  which  arise  (those  of  the  antennae  excepted) 
from  small  tubercules  situated  in  the  middle  of  a  small,  FlG-  2.-c»romopfci»  jug- 
-..  i  i  i  •  i  .  •  landicola:  Stem-mother,  newly 

circular,  dusky  area.     Antennae  3-jomted,  the  distal  joint     jacked     (Original ) 
the  largest.    Cornicles  very  small,  erect.     Cauda  almost  as 

long  as  the  hind  tarsus,  its  apex  blunt.  Cornicles  and  cauda  concolorous  with  the 
abdomen.  Beak  very  pale,  reaching  second  coxae,  its  extreme  apex  brown.  Under- 
side of  the  head  very  pale  yellow;  of  the  abdomen  greenish -yellow. 

THE  STEM-MOTHER;  AFTER  FIRST  MOLT  AND  JUST  PREVIOUS  TO  SECOND  MOLT. 

Pale  lemon-yellow  or  yellowish  green,  flatly  oval,  closely  appressed  to  the  plant 
surface,  occurring  on  the  underside  of  the  expanding  leaves,  between  the  ribs. 
Antennae  and  legs  very  pale  yellow,  almost  hyaline.  Antennae  short,  reaching  slightly 
beyond  the  posterior  margin  of  the  prothorax,  3-jointed,  with  a  rudimentary  suture 
on  the  distal  half  of  joint  III .  This  joint  is  about  three  times  as  long  as  the  two  proxi- 
mal joints  together.  Eyes  crimson,  not  fully  developed.  Legs  entirely  pale,  with- 
out any  trace  of  dark  knee  spots.  Thorax  and  segments  1  to  6  of  the  abdomen  with  two 
longitudinal  rows  of  black  or  brown  spots,  on  each  of  which  occurs  a  small  pale  tubercle 
bearing  two  capitate  hairs,  one  larger  than  the  other.  On  the  thoracic  segments  and 
on  abdominal  segments  1  to  7  occur  two  rows  of  pale  lateral  tubercles,  each  of  which 
bears  three  capitate  hairs.  The  frontal  margin  of  the  head  bears  six  such  hairs  on 
tubercles.  Antennal  joints  I  and  II  with  a  capitate  hair  on  their  inner  margins  near 
the  middle,  and  joint  III  with  one  such  hair  on  the  inner  margin  near  the  base.  The 
eighth  abdominal  segment  bears  a  dorsal  fringe  of  six  capitate  hairs,  those  on  either 
end  being  smaller  than  the  four  inner  ones.  Cornicles  situated  on  segment  6,  as  broad 
as  long,  erect,  concolorous  with  the  abdomen.  Cauda  without  armature,  bluntly  coni- 
cal, almost  hyaline,  about  as  long  as  the  hind  tarsus.  Beak  barely  reaching  second 
coxae ,  pale  yellow,  the  extreme  tip  brown .  Measurements :  Length  of  body ,  1 . 55  mm . ; 
width,  0.775  mm.;  antenna,  joint  I,  0.  053  mm.;  joint  II,  0:048  mm.;  joint  III,  0.304 
mm. 

Described  from  specimens  collected  at  San  Jose,  Cal.,  March  28, 
1912. 


6  BULLETIN  100,   U.   S.   DEPARTMENT  OF   AGRICULTURE. 

After  the  second  molt  the  spines  on  the  dorsum  of  the  body  disap- 
pear.    (See  fig.  3.) 

The  pupal  and  imaginal  stages  of  the  stem-mother  show  no  appar- 
ent difference  in  respect  to  size,  color,  or  structure  from  those  of  the 

later  viviparous  generations,  and  thus 
one  description  of  these  forms  will  suf- 
fice for  all  the  winged  viviparous  gen- 
erations. 

THE    PUPA    OF  THE    WINGED    VIVIPAROUS 
FEMALE    (FIG.   4). 

General  color  pale  lemon-yellow.  Eyes  red, 
fully  formed.  Antennae  reaching  a  little  be- 
yond the  base  of  the  wing-pads,  pale,  joint  III 
the  longest,  joints  IV  and  V  subequal.  Ocelli 
present.  Anterior  margin  of  the  head  bearing 
six  capitate  spines.  Thoracic  segments  pale 
yellow.  Wing-pads  pale  yellow,  closely  ap- 
pressed  to  the  sides  of  the  body.  Legs  pale 
FIG.  3.— Chromaphis  jv^landkola:  Larva  of  yellow,  with  the  dark  knee  spot  on  the  hind 
stem-mother  after  second  molt.  (Grig-  fem0ra  only;  tarsi  dusky.  Abdomen  oval,  pale 
lemon-yellow,  with  a  varying  number  of  dark 

spots  on  the  dorsum,  which  spots  are  always  present  on  segment  5  but  often  lacking  on 
the  other  segments.  Head,  thorax,  and  abdomen  furnished  with  lateral  rows  of  capi- 
tate hairs  which  stand  on  small  pale  tubercles.  Cornicles  small,  as  wide  aa  long, 
slightly  constricted  in  the  middle,  situated  on  the  sixth  abdominal  segment.  Cauda 
short,  about  as  long  as  the  cornicles,  bluntly  rounded  at  the  apex.  Cornicles  and 
cauda  concolorous  with  the  body.  Beak  short,  pale,  stout,  reaching  to  the  first  pair  of 
coxae.  The  pupa  has  the  legs  relatively  a  little  shorter  than  those  of  the  adult  and  ia 
thus  more  closely  appressed  to  the  leaf  s  tirf  ace .  The 
body  is  quite  flat.  Measurements:  Length  of  body, 
1.87  mm.  (average);  width,  0.85  mm.  (average  max- 
imum); antenna,  joint  I,  0.050  mm.;  joint  II, 
0.042  mm.;  joint  III,  0.183  mm.;  joint  IV,  0.081 
mm.;  joint  V,  0.076  mm.;  joint  VI,  0.065  mm.; 
filament,  0.034  mm.  Cornicles,  0.04  mm. 

The  stem-mothers  pass  through  the 
pupal  molt  about  one  week  before  the  final 
molt  takes  place,  and  after  the  latter  they 
acquire  their  full  development  as  winged 
adults.  In  the  latter  generations  the 
pupal  instar  occupies  from  three  to  six 
days. 

THE  WINGED  VIVIPAROUS  FEMALE   (FIG.  5).  Fio.    4.—  Chromaphis  juylandicola: 

Pupa  of  winged   viviparous  fe- 

General  color  pale  lemon-yellow;  many  Individ-         maie    (Original ) 
uals  are  darker  yellow,  yellowish-brown,  or  salmon- 
pink.    Antennae    on    very   small   frontal    tubercles,    about   one-half   the   length 
of  the  body,  yellow,  with  the  inner  lateral  margins  of  the  first  two  joints  dusky; 
articulations  of  joints  III  to  VI  and  the  whole  filament  dusky  to  black.    Eyes  red. 
Ocelli  present.     Prothorax  yellow.     Thoracic  lobes  and  scutellum  light  brown,  some- 
times greenish-yellow,  pale  yellow  in  newly-molted  individuals.     Wings  of  medium 


WALNUT  APHIDES  IN   CALIFORNIA.  7 

size;  subcosta  and  wing  insertions  pale  yellow;  stigma  pale  gray,  with  a  darker  area 
at  the  confluence  of  the  third  discoidal  vein,  and  another  such  though  smaller  area  at 
the  apex;  veins  rather  heavy,  dark  brown,  all  three  discoidals  arising  from  the  sub- 
costa and  thickened  at  their  bases;  second  branch  of  third  discoidal  nearer  the  wing 
apex  than  the  first  fork;  third  discoidal  describing  a  regular  gentle  curve  for  its  entire 
length;  stigmatic  vein  entire,  the  depth  of  its  curve  varying  in  different  examples, 
generally  reaching  the  wing  margin  midway  between  the  apex  of  the  stigma  and  the 
the  end  of  the  third  discoidal  (often  it  touches  the  margin  considerably  nearer  the 
stigma,  but  rarely  nearer  the  third  discoidal) .  Legs  rather  Aort,  but  a  little  longer  than 
those  of  the  pupa;  front  pair  yellow  with  the  tarsi  and  apical  third  of  the  tibiae  dusky 


FIG.  5. —  Chromaphis  juglandicola:  Wingad  viviparous  female  (appendages  of  left  side  removed),    a, 
Left  antenna;  6,  right  cornicle;  c,  front  tarsus.    (Original.) 

gray  and  the  knee  spot  rarely  present  (gray  when  present);  middle  pair  yellow,  with 
an  indefinite  gray  spot  on  the  upper  side  of  the  femur  above  the  knee  and  with  the 
tarsi  dusky  gray;  hind  pair  yellow,  with  a  coal-black  spot  (sometimes  produced  into 
an  annulation)  on  the  upper  side  of  the  femur  above  the  knee  joint  and  with  the  tarsi 
dusky  gray  as  in  the  other  pairs.  The  knee  spots  are  always  present  on  the  hind 
femora,  while  they  occur  in  about  80  per  cent  of  individuals  on  the  middle  femora. 
In  35  individuals  examined  throughout  the  year  all  had  the  spots  on  the  hind  femora, 
28  had  spots  on  the  middle  femora,  and  only  1  had  spots  on  the  fore  femora.  Abdomen 
pale  lemon-yellow,  widest  at  segment  3,  considerably  wider  than  the  thorax,  gen- 
erally bearing  two  oval  brown  spots  on  segment  5  and  more  rarely  with  two  similar  but 
smaller  spots  onsegment4;  occasionally  immaculate.  These  spots  are  sometimes  gray- 
ish, varying  in  intensity,  and  appear  to  be  the  pupal  markings  retained  in  the  adult  form. 


8  BULLETIN  100,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

Cornicles  (fig.  5,  6)  pale  yellow,  constricted  in  the  middle,  barely  as  long  as  broad. 
Abdominal  segments  3  to  6  inclusive  bearing  pale  lateral  tubercles.  Body  without 
hairs.  Cauda  very  pale,  globular,  about  as  long  as  the  cornicles.  Beak  pale  yellow, 
the  extreme  tip  black,  reaching  a  little  beyond  the  first  coxae.  Sternum  pale  brown. 
Measurements:  Length  of  body,  1.62-2.55  mm.,  average  2.08  mm.;  width  of  body  at 
segment  3  of  abdomen,  0.71-1.06  mm.,  average  0.88  mm.;  wing  expanse,  4.42-5.21 
mm.,  average  4.77  mm.;  antenna,  joint  I,  0.046-0.067  mm.,  average  0.055  mm.;  joint 
II,  0.039-0.055  mm.,  average  0.043  mm.;  joint  III,  0.267-0.408  mm.,  average  0.337 
mm.;  joint  IV,  0.153-0.233  mm.,  average  0.196.mm.;  joint  V,  0.133-0.191  mm.,  aver- 
age 0.162  mm.;  joint  VI,  0.079-0.094  mm.,  average  0.083  mm.;  antennal  filament, 
0.038-0.043  mm.,  average  0.040  mm.;  total  length  of  antenna,  0.775-1.060  mm.,  aver- 
age 0.916  mm.;  cornicles,  0.05  mm.;  cauda,  0.056  mm. 

There  are  from  6  to  8  transverse  oval  sensoria  on  antennal  joint  III,  1  terminal  sen- 
sorium  on  joint  V,  and  three  terminal  ones  on  joint  VI.  Buckton's  measurements 
(Buckton,  1872)  seem  to  have  been  taken  from  small  examples  for,  with  the  exception 
of  those  of  the  antennal  joints,  his  measurements  are  all  smaller  than  the  average  found 
by  the  writer.  It  may  be  that  California  examples  are  larger  than  the  European. 

Within  a  few  hours  after  the  last  molt  the  wings  harden  and  the  chitin 
stiffens.  The  stem-mothers  then  begin  to  deposit  the  young  that 
have  been  visible  as  pseudova  for  a  week  or  longer  inside  their  bodies. 
In  the  life-history  experiments  the  greatest  number  of  young  pro- 
duced by  one  viviparous  female  was  44.  These  were  extruded  from 
the  body  in  20  days,  30  in  the  first  half  and  14  in  the  last  half  of  that 
period.  Several  adults  under  observation  deposited  11  or  12  young 
within  12  hours  after  reaching  maturity,  and  no  more  after  that, 
dying  with  many  unborn  pseudova  in  their  bodies.  In  the  field 
the  aphides  deposit  all  their  young  on  one  leaf  or  on  several  leaves 
near  one  another.  The  average  number  of  young  deposited  by  a  single 
adult  ranges  between  25  and  35.  This  seems  to  be  about  the  same  as 
in  other  closely  related  Callipterini,  but  is  a  much  smaller  number 
than  that  occurring  in  members  of  other  tribes  of  Aphididse.  The 
aphides  of  the  fall  viviparous  generation  produce  fewer  young, 
those  which  develop  in  November  depositing  only  6  or  8.  As  many 
as  30  oval  unborn  aphides  may  be  seen  in  the  body  of  one  recently 
molted  female.  These  embryos  vary  in  size,  only  those  to  be  de- 
posited immediately  being  fully  grown.  Each  is  inclosed  in  a  very 
thin  hyaline  sac  in  which  they  are  contained  at  birth. 

The  newly  deposited  young  of  the  second  and  subsequent  genera- 
tions, both  viviparous  and  oviparous,  differ  from  the  infant  stem- 
mothers  in  that  they  are  entirely  pale  yellow  (rarely  suffused  with  a 
faint  pink)  and  remain  thus  until  the  first  molt,  while  the  young 
stem-mothers  have  dusky  appendages  and  abdominal  spots.  The 
young  deposited  by  the  stem-mothers  pass  through  their  first  molt 
in  from  three  to  six  days.  After  this  molt  there  appear  brown  or 
black  dorsal  spots  in  the  majority  of  the  individuals,  and  these 
markings  persist  through  the  succeeding  molts.  A  small  percentage 


WALNUT  APHIDES  IN   CALIFORNIA. 


9 


of  examples  remain  immaculate  throughout  development.  The 
"lice"  of  the  second  generation  develop  more  quickly  than  the  stem- 
mothers  or  first  generation,  owing  to  greater  abundance  of  food 
supply  and  to  the  higher  temperature  existing  at  that  later  period. 
In  1911  second-generation  young  were  deposited  in  the  field  on 
early  varieties  of  walnuts  a  little  before  April  23,  while  in  the  following 
year  these  were  deposited  as  early  as  April  6.  This  is  to  be  expected, 
since  in  1912  the  trees  came  out  in  leaf  two  weeks  earlier  than  in  the 
previous  year.  Table  II  shows  the  life  cycle  of  41  individuals  of  the 
second  generation  at  San  Jose,  Cal.,  in  1911. 

TABLE  II. — Life  cycle  of  the  second  generation  of  Chromaphis  juglandicola,  San  Jose, 

Cal.,  1911. 


Date  of— 

Date  of— 

No.  of 
individ- 
ual. 

Life 
cycle. 

No.  of 
individ- 
ual. 

Life 
cycle. 

Deposi- 
tion. 

Acquiring 
wings. 

Deposi- 
tion. 

Acquiring 
wings. 

1.... 

Apr.  23 

May  12 

Days. 
19 

22  

May     2 

May  22 

Days. 
20 

2  

23 

12 

19 

23  

2 

22 

20 

3  

23 

14 

21 

24  

3 

22 

19 

4  

23 

16 

23 

25  

3 

22 

19 

5  

23 

18 

25 

26  

3 

22 

19 

6  

24 

18 

24 

27  

3 

22 

19 

7  

24 

18 

24 

28  

3 

22 

19 

8  

24 

18 

24 

29  

4 

23 

19 

9  

24 

18 

24 

30  

4 

23 

19- 

10  

24 

18 

24 

31  

5 

25 

20 

11  

25 

20 

25 

32.   ..   . 

5 

25 

20 

12  

28 

21 

25 

33.   ..   . 

5 

25 

20 

13.   .   .. 

May     1 

21 

20 

34.   -.   . 

6 

26 

20 

14.   .   .. 

1 

21 

20 

6 

26 

20 

15.   .   .. 

1 

21 

20 

se!!!!  ! 

6 

27 

21 

16.   .   .. 

1 

21 

20 

37  

6 

27 

21 

17.   -   .. 

1 

21 

20 

6 

27 

21 

18.  .  .. 

2 

21 

19 

39!!!! 

7 

27 

20 

19.   .   .. 

2 

21 

19 

40  

8 

28 

20 

20.   .   .. 

2 

22 

20 

41  

9 

27 

18 

21.   .   .. 

2 

22 

20 

Life  cycle: 

Maximum. . . 
Minimum — 
Average 


Days. 
25 
18 
20.7 


The  aphides  of  the  third  generation  appear  on  the  earliest  varieties 
of  walnuts  about  the  middle  of  May,  but  on  the  late  varieties  such 
as  the  Franquette  this  brood  appears  as  much  as  a  month  later.  The 
individuals  of  this  generation  are  on  the  average  slightly  larger  than 
those  of  other  generations .  In  a  large  series  of  adult  viviparous  females 
taken  throughout  the  year  of  1911  the  largest  example  was  of  the  third 
generation.  Its  body  was  2.55  mm.  in  length  and  1.06  mm.  in  width, 
and  both  of  its  antennae  measured  1.06  mm.,  or  0.02  mm.  in  excess 
of  the  next  longest  antenna  in  the  series.  Table  III  indicates  the  life 
cycle  of  97  individuals  of  the  third  generation. 
40859°— Bull.  100—14 2 


10 


BULLETIN  100,   U.   S.   DEPARTMENT  OF   AGRICULTURE. 


TABLE  III. — Life  cycle  of  the  third  generation  of  Chromaphis  juglandicola,  San  Jose, 

Cal,  1911. 


Date  of— 

Date  of- 

No.  of 
indi- 
vidual. 

Depo- 
sition. 

Acquir- 
ing 

wings. 

Life 
cycle. 

No.  of 
indi- 
vidual. 

Depo- 
sition. 

Acquir- 
ing, 
wings. 

Life 
cycle. 

1 

May  19 

June 

Days. 
16 

50.... 

May  19 

June  7 

Days. 
19 

2!".! 

19 

16 

51  

19 

7 

19 

3  

19 

16 

52  

19 

7 

19 

4  

19 

16 

53  

19 

7 

19 

5  

19 

17 

54  

19 

7 

19 

6  

19 

17 

55  

19 

7 

19 

7  

19 

5 

17 

56  

19 

7 

19 

8  

19 

5 

17 

57  

19 

8 

20 

9  

19 

5 

17 

58  

19 

8 

20 

10  

19 

5 

17 

59  

19 

8 

20 

11  

19 

5 

17 

60  

19 

8 

20 

12  

19 

5 

17 

61  

19 

8 

20 

13  

19 

5 

17 

62  

19 

8 

20 

14  

19 

5 

17 

63  

19 

8 

20 

15  

19 

5 

17 

64  

19 

8 

20 

16  

19 

5 

17 

65  

19 

9 

21 

17  

19 

5 

17 

66  

19 

9 

21 

18  

19 

6 

18 

67  

22 

10 

19 

19  

19 

6 

18 

68  

22 

11 

20 

20  

19 

6 

18 

69  

22 

11 

20 

21  

19 

6 

18 

70  

22 

11 

20 

22  

19 

6 

18 

71  

22 

11 

20 

19 

6 

18 

72  

22 

11 

20 

24!!!! 

19 

6 

18 

73  

22 

11 

20 

25  

19 

6 

18 

74  

22 

11 

20 

26  • 

19 

6 

18 

75  

22 

11 

20 

27  

19 

6 

18 

76  

22 

11 

20 

28  

19 

6 

18 

77  

22 

11 

20 

.29  

19 

6 

18 

78  

22 

11 

20 

30  

19 

6  • 

18 

79  

22 

11 

20 

31  

19 

6 

18 

80  

22 

11 

20 

32  

19 

6 

18 

81  

22 

11 

20 

33  

19 

6 

18 

82  

22 

11 

20 

34  

19 

6 

18 

83  

22 

11 

20 

35  

19 

6 

18 

84  

22 

12 

21 

36  

19 

6 

18 

85  

22 

12 

21 

37  

19 

6 

18 

86  

22 

12 

21 

38  

19 

6 

18 

87  

22 

12 

21 

39  

19 

6 

18 

88  

22 

12 

21 

40  

19 

6 

18 

89  

22 

12 

21 

41  

19 

6 

18 

90  

22 

13 

22 

42  

19 

6 

18 

91  

22 

13 

22 

43  

19 

7 

19 

92  

22 

13 

22 

44  

19 

7 

19 

93  

22 

14 

23 

45  

19 

7 

19 

94  

22 

14 

23 

46  

19 

7 

19 

95  

22 

14 

23 

47  

19 

7 

19 

96  

22 

15 

24 

48  

19 

7 

19 

97  

22 

15 

24 

49  

19 

7 

19 

Life  cycle:  Days. 

Maximum 24 

Minimum 16 

Average 19. 1 

Generations  IV  to  VIII  inclusive  occupy  roughly  16  days  apiece 
for  development,  and  this  period  is  the  average  life  cycle  during  the 
summer  months.  Some  aphides  will  develop  in  14  days  and  others 
in  19  or  20.  Table  IV  gives  the  life-cycle  records  of  these  five  genera- 
tions and  also  that  of  the  ninth.  The  records  hi  some  instances  are 
small,  but  the  fact  that  in  the  first  five  of  these  generations  there  is 
practically  no  difference  in  the  duration  of  the  life  cycle  was  cor- 
roborated by  a  larger  series  of  experiments  during  the  summer  months 
with  individuals  of  which  the  respective  generations  were  unknown. 


WALNUT  APHIDES  IN   CALIFORNIA. 


11 


TABLE  IV. — Life  cycle  of  the  summer  generations  of  Chromaphis  juglandicola,  San  Jose 

Cal,  1911. 


Date  of— 

Generation  No. 

No.  indi- 
vidual. 

Deposi- 
tion. 

Reach- 
ing adult 
state. 

Life 

cycle. 

Form  of  indi- 
vidual. 

Day.". 

1 

June     8 

June  28 

20 

Viviparous. 

2 

16 

July     1 

15 

60. 

3 

16 

1 

15 

Do. 

IV 

4 

16 

1 

15 

Do. 

5 

16 

2 

16 

Do. 

6 

16 

2 

16 

Do. 

7 

16 

2 

16 

Do. 

1 

July     1 

15 

14 

Do. 

V  

2 

j 

15 

14 

Do. 

3 

1 

17 

16 

Do. 

4 

1 

18 

17 

Do. 

1 

15 

31 

16 

Do. 

2 

15 

31 

16 

Do. 

3 

15 

31 

16 

Do. 

4 

15 

31 

Id 

Do. 

5 

15 

31 

16 

Do. 

6 

15 

31 

16 

Do. 

7 

15 

31 

16 

Do. 

8 

16 

Aug.     1 

16 

Do. 

9 

16 

1 

16 

Do. 

10 

16 

1 

16 

Do. 

VI 

11 

16 

2 

17 

Do. 

12 

16 

2 

17 

Do. 

13 

16 

2 

17 

Do. 

14 

16 

2 

17 

Do. 

15 

17 

2 

16 

Do. 

16 

17 

2 

16 

Do. 

17 

17 

2 

16 

Do. 

18 

17 

3 

17 

Do. 

19 

17 

4 

18 

Do. 

20 

18 

5 

18 

Do. 

21 

18 

6 

19 

Do. 

22 

18 

6 

19 

Do. 

1 
2 

Aug.    2 

17 

17 

15 
15 

Do. 
Do. 

VII 

3 

2 

17 

15 

Do. 

4 
5 

2 
3 

19 
20 

17 
17 

Do. 
Do. 

6 

3 

20 

17 

Do. 

7 

3 

20 

17 

Do. 

1 

2 

IS 
19 

Sept.    1 

14 
14 

Do. 
Oviparous. 

3 

19 

2 

14 

t>0. 

4 

19 

3 

15 

Do. 

5 

19 

3 

15 

Do. 

6 

19 

3 

15 

Do. 

7 

19 

3 

15 

Do. 

8 

19 

3 

15 

Do. 

VIII 

9 

19 

3 

15 

Do. 

10 

20 

4 

15 

Do. 

11 

20 

4 

15 

Do. 

12 

20 

4 

15 

Do. 

13 

20 

6 

17 

Viviparous. 

14 

20 

6 

17 

Oviparous. 

15 

20 

6 

17 

So. 

16 
1 

20 

Sept.    5 

7 
30 

18 
25 

Viviparous. 
Oviparous. 

2 

5 

Oct.     1 

26 

So. 

3 

5 

6 

31 

Viviparous. 

4 

5 

6 

31 

60. 

5 

5 

8 

33 

Do. 

6 

5 

8 

33 

Do. 

7 

7 

9 

32 

Do. 

IX 

8 

7 

11 

34 

Do. 

9 

7 

13 

36 

Do. 

10 

7 

14 

37 

Do. 

11 

7 

14 

37 

Do. 

12 

8 

12 

34 

Do. 

13 

8 

17 

39 

Do. 

14 

8 

17 

39 

Do. 

12  BULLETIN   100,   U.    S.   DEPARTMENT  OF   AGRICULTURE. 

An  inspection  of  Table  IV  shows  that  the  length  of  the  life  cycle 
of  Generations  IV  to  VII  was  almost  the  same.  This  is  to  be  ex- 
pected, since  in  1911  the  months  of  June,  July,  and  August  had 
almost  identical  temperatures  both  day  and  night.  It  will  also  be 
observed  that  there  was  a  very  noticeable  difference  between  the  life- 
cycle  periods  of  Generations  VIII  and  IX,  16  individuals  of  the  eighth 
generation  averaging  15.4  days  and  14  individuals  of  the  ninth  gen- 
eration averaging  33.4  days.  The  ninth  generation  thus  required 
for  development  a  period  over  twice  as  long  as  that  required  by  the 
preceding  generation,  developing  almost  as  slowly  as  the  stem 
mother  generation  (see  Table  I).  Yet  the  temperature  during  the 
daytime  influencing  the  ninth  generation  differed  but  little  from 
those  which  obtained  during  the  development  of  the  eighth.  The 
probable  causes  of  the  slow  development  of  the  ninth  generation  lice 
is  to  be  found  in  the  colder  night  temperatures  to  which  they  were 
subjected  and  in  the  fact  that  the  leaves  at  this  time  are  becoming 
less  vigorous  and  consequently  afford  poorer  nourishment  for  the 
aphides  than  earlier  in  the  season.  There  is  a  tenth  generation,  and 
in  warm  early  seasons  probably  an  eleventh,  but  in  these  generations 
the  brood  is  small  and  the  "lice"  grow  slowly.  Plant  lice  may  be 
found  in  early  December  giving  birth  to  young,  which  are  destined 
to  perish  either  when  the  leaves  drop  or  through  exposure  to  hard 
frost.  The  author  has  observed  dead  aphides  of  all  sizes  on  the 
brown  frosted  leaves  during  early  winter. 

All  the  plant  lice  used  for  the  life-history  experiments  were  reared 
out  of  doors  on  young  seedling  walnut  trees  planted  in  pots  and  in- 
closed with  glass  cylinders.  In  1911  the  stock  was  procured  from 
stem  mothers  collected  on  the  earliest  varieties  of  walnuts.  When 
the  work  was  started  in  1911  it  was  too  late  to  procure  eggs,  and  so 
the  data  on  the  stem-mother  cycle  was  acquired  in  1912. 

After  the  ninth  generation  no  more  life-history  experiments  were 
carried  on  in  the  rearing  cages,  but  a  weekly  examination  was  made 
of  infested  leaves  in  the  field  to  determine  the  proportions  of  tho  dif- 
ferent forms,  sexual  and  asexual,  during  the  fall  months. 

THE  OVIPAROUS  OR  SEXUAL  FORMS. 

The  oviparous  forms  are  the  true  sexes,  comprising  the  winged 
male  and  the  wingless  oviparous,  or  egg-producing,  female.  The 
female  aphis,  after  fertilization  by  the  male,  deposits  true  eggs,  in 
which  form  alone  the  insect  can  tide  over  the  winter  months  when 
no  food  supply  is  procurable. 

As  is  shown  in  Table  IV,  there  is  no  real  oviparous  generation,  for 
in  all  the  later  or  fall  generations  a  certain  percentage  of  the  young 
will  develop  either  into  the  sexed  males  or  the  sexed  females.  On 
heavily  infested  trees  oviparous  aphides  appear  as  early  in  the  season 


WALNUT   APHIDES   IN    CALIFOENIA. 


13 


as  July,  while  on  trees  attacked  by  few  lice  these  forms  will  not  occur 
until  September  or  October.  It  therefore  seems  that  the  more 
heavily  a  tree  is  infested  the  earlier  will  the  sexed  forms  be  produced. 
A  glance  at  Table  IV  demonstrates  that  the  first  oviparous  form 
of  the  life-cycle  material  became  adult  September  2,  and  was  a 
member  of  the  eighth  generation.  In  the  field  the  first  oviparous 
form  was  observed  in  1911  on  July  7,  and  in  1912  on  July  9.  Both  of 
these  occurred  on  early-leafing  trees  and  probably  belonged  to  the  fifth 
or  sixth  generation.  As  the  growth  of  the  aphis  colony  may  be  said  to 
have  reached  its  zenith  about  the  middle  of  July,  it  is  at  the  time  of 
its  greatest  abundance  that  the  sexed  individuals  begin  to  appear. 
And,  indeed,  for  the  welfare  of  the  species  they  appear  none  too 
soon,  for  it  is  in  July  and  August  that  the  hordes  of  natural  enemies 
work  tremendous  havoc,  frequently  cleaning  up  a  bad  infestation  on 
a  tree  within  three  weeks.  Those  sexual  females  that  have  gone  to 
the  trunk  and  limbs  to  deposit  their  eggs  very  often  escape  destruc- 
tion while  the  others  remaining  on  the  foliage  are  devoured.  Until 
the  middle  of  August  the  sexual  forms  are  comparatively  rare  and 
comprise  less  than  5  per  cent  of  the  whole,  but  after  that  time  they 
become  more  and  more  abundant.  The  sexed  females  always  greatly 
outnumber  the  males.  Table  V  indicates  the  advance  and  decline 
of  the  sexual  forms  in  the  late  summer  and  fall.  The  data  were  ob- 
tained by  weekly  visits  to  badly  infested  trees,  during  which  the 
lice  on  a  certain  number  (50)  of  leaflets  picked  out  at  random  were 
counted.  It  must  be  borne  in  mind  that  as  the  fall  advances  more 
and  more  sexual  females  repair  to  the  limbs  for  the  purpose  of  depos- 
iting their  eggs,  and  that  therefore  in  the  case  of  the  later  counts  a 
really  greater  proportion  of  these  were  present  on  the  trees  than 
would  appear  from  the  records. 

TABLE  V. —  Comparative  numbers  of  sexual  and  asexual  forms  of  Chromaphisjuglandicola 
observed  on  the  foliage  at  different  dates,  San  Jose,  CaL,  1911. 


Date  of  collection. 

Number  of  — 

Percent- 
age of  — 

Vivipa- 
rous 
forms. 

Ovipa- 
rous 
forms. 

Males. 

Vivipa- 
rous 
forms. 

September  15  ... 

241 
258 
203 
171 
166 
207 
172 
420 
233 
10 

247 
355 
H3 
66 
74 
117 
111 
80 
36 
0 

4 
5 
6 
9 
14 
9 
4 
11 

0 

49 
42 
58 
70 
65 
02 
60 
82 
84 
100 

23  

30 

October  7 

14..                                         

g 

16 

23  

Total 

2,081 

1,229 

69 

""ei.'e 

14 


BULLETIN  100,   U.   S.   DEPARTMENT  OF   AGRICULTURE. 


The  maximum  number  of  aphides  found  on  a  single  leaflet  through- 
out the  counts  was  90,  of  which  64  were  sexual  females.  This  oc- 
curred on  the  first  date  of  collection. 

It  will  be  noticed  from  Table  V  that  on  the  first  two  dates  the  ovi- 
parous forms  were  predominant  but  that  on  all  later  dates  these  were 
outnumbered  by  the  viviparous  individuals.  On  the  date  of  the 
fourth  collection  (October  7)  numerous  sexual  females  were  found  on 
the  limbs  of  the  tree,  and  their  number  was  more  and  more  augmented 
each  succeeding  week.  About  October  1  the  males  appeared  in  num- 
bers, very  few  of  them  having  been  in  evidence  previous  to  this  time, 
although  the  first  male  of  the  season  was  noticed  July  10.  Table  VI 
indicates  the  preponderance  in  numbers  of  the  sexual  female  over 
the  male. 

TABLE  VI.— Preponderance  of  the  sexual  female  of  Chromaphis  juglandicolaover  themale. 


Date  of  collection  or  count. 

Number  of 
sexual 
females  to 
each  male. 

Date  of  collection  or  count. 

Number  of 
sexual 
females  to 
each  male. 

September  15 

62 

October  24  

13 

71 

November  2 

28 

30 

24 

9 

October  7 

7.3 

16  

5 

14 

5.3 

23... 

(i) 

i  None  of  either  sex  seen  on  leaves. 


Table  VI  was  compiled  from  the  same  material  as  that  used  for 
Table  V.  On  November  9  nearly  all  the  sexual  females  were  clus- 
tered on  the  limbs,  and  two  weeks  later  they  and  all  other  plant  lice 
at  the  experimental  trees  succumbed  to  a  severe  frost,  which  had 
at  the  same  time  withered  all  the  leaves.  This  clustering  of  the 
sexual  females  or  sexuparse  about  the  limbs  explains  the  small  per- 
centage of  this  form  as  compared  with  the  males  on  November  9 
and  16. 

Copulation  seems  to  occur  only  on  the  leaf,  and  the  females  are  not 
fertilized  until  they  have  passed  through  the  last  molt.  A  single 
male  may  fertilize  several  females — probably  quite  a  large  number 
when  it  is  considered  that  the  latter  sex  so  greatly  outnumbers  the 
former  and  that  very  few  eggs  prove  infertile.  Copulation  in  all 
instances  observed  by  the  writer  occupied  some  30  seconds  of  time — 
a  very  short  p^iod  for  an  aphis.  If  the  male  be  disturbed,  he  will 
immediately  retract  his  genital  organ  and  move  off.  In  1912  the 
males  appeared  in  comparative  abundance  in  the  vicinity  of  San 
Jose  as  early  as  August  26. 

In  general  appearance  the  adult  oviparous  female  differs  from  the 
viviparous  form  in  that  it  is  wingless,  has  a  wider  body,  and  bears 
three  conspicuous  transverse  brown  or  black  bands  on  the  dorsum 
of  the  abdomen.  The  male  is  greenish-yellow,  winged,  with  black 


WALNUt    APHIDES   IN    CALIFORNIA. 


15 


Or  dusky  gray  legs  and  antennae.  The  oviparous  or  sexual  female 
molts  four  times  but  does  not  differ  in  appearance  from  the  viviparous 
form  until  the  third  molt  is 


FIG.  6. —  Ckromaphis  juglandicola:  Oviparous 
female,  penultimate  instar.    (Original.) 


THE   OVIPAROUS  FEMALE,   AFTER  THE  THIRD  MOLT  (FIG.   6)< 

Rather  smaller  and  narrower  than  the  full-grown  form.     General  color  pale  gamboge* 

yellow,  sometimes  lemon  yellow.     Body  twice 

as  long  as  wide.     Eyes  bright  red.     Head  with 

six  erect,  capitate  spines  on  the  anterior  margin. 

Antennae  short,  reaching  barely  to  the  middle  of 

the  mesothorax;  7-jointed,  joint  III  the  longest, 

joints  IV  and  V  subequal,  joint  VI  longer  than 

its  spur  or  filament.  Spur  dusky,  rest  of  anten- 
nae pale  lemon  yellow.  Head,  thorax,  and  ab- 
domen with  two  longitudinal  rows  of  oval  black 

spots  on  the  dorsum.     Thorax  and  abdominal 

segments  1-5  with  two  lateral  longitudinal  rows 

of  circular  black  spots,  on  which  are  situated 

small  tubercles  bearing  capitate  hairs.     Such 

tubercles  also  occur  on  the  black  dorsal  spots. 

Eighth  segment  of  the  abdomen  unmarked, 

bearing  on  its  posterior  margin  a  fringe  of  six 

capitate  hairs.     Legs  pale  greenish-yellow  with 

the  characteristic  knee  spot  on  the  hind  femora 

only;  tarsi  gray.     Cornicles  on  the  sixth  segment,  quite  small,  wider  than  long,  pale 

lemon-yellow.     Cauda  equal  in  length  to  the  hind  tarsus,  pale  yellow,  rounded.     Beak 

very  pale,  almost  white,  reaching  to  the  anterior  coxae.  Measurements:  Length  of 

body,  1.51  mm.;  width  of  body,  0.76 
mm.;  antennae,  joint  I,  0.063  mm.; 
joint  II,  0.048  mm.;  joint  III,  0.136 
mm.;  joint  IV,  0.083  mm.;  joint  V, 
0.085  mm. ;  joint  VI,  0.086  mm. ;  fila- 
ment, 0.021  mm. 

Described  from  specimens 
collected  at  Walnut  Creek,  CaJ., 
and  San  Jose,  Cal.,  October  16 
to  26,  1912. 


THE  OVIPAROUS  FEMALE,  ADULT  STAGE 
(FIG.  7). 

General  color  gamboge,  varying  in 
newly  molted  examples  to  lemon  yel- 
low and  in  older  individuals  to  salmon 
pink  or  with  a  distinct  brownish  tint. 
Eyes  crimson.  Head  and  prothorax 
with  indefinite  dusky  brown  markings. 
Ocular  tubercles  small.  Anterior  mar- 
gin of  the  head  with  six  capitate  hairs 
projecting  forward.  Thorax  mottled  all  over  with  shades  of  brown,  its  lateral  margins 
lighter.  Prothorax  with  two  capitate  hairs  on  either  side  of  its  posterior  portion.  Ab- 
domen with  two  or  three  hairs  on  the  lateral  margins  of  each  segment.  Segments  4  and 
5  and  posterior  half  of  3  with  dark  brown  or  black  markings  which  generally  coalesce  to 


-  Chromaphis  juglandicola:  Oviparous  female. 
Right  antenna.    (Original.) 


16  BULLETIN   100,   U.    S.   DEPARTMENT  OP   AGRICULTURE. 

form  three  transverse  bars  or  bands,  of  which  those  on  segments  4  and  5  do  not  quite  reach 
the  lateral  margins  of  the  segments,  while  that  on  the  third  segment  is  slightly  shorter 
and  but  half  as  broad  as  the  others.  Wings  absent.  Cornicles  quite  similar  to  those  of 
the  winged  viviparous  female.  Cauda  globular,  concolorous  with  the  abdomen,  larger 
than  that  of  the  winged  viviparous  female.  Anal  plate  large,  U-shaped,  extending 
beyond  the  cauda  when  viewed  from  above.  In  reality  it  has  a  shallow  incision  at 
the  apex.  Antennae  on  slight  frontal  tubercles,  reaching  to  the  middle  of  the  meta- 
thoracic  segment,  white,  with  the  apices  of  joints  3  to  6  black.  Legs  very  pale  yellow, 
almost  hyaline;  tarsi  dusky  gray  at  their  apices.  All  six  femora  have  the  character- 
istic black  or  brown  knee  spot.  Beak  yellow,  the  extreme  tip  black,  reaching  to  the 
second  coxae.  Hind  tibiae  not  much  swollen,  bearing  about  35  circular  sensoria 
occurring  evenly  on  the  middle  two-thirds  of  the  tibia  and  arranged  in  an  irregular 
Bpiral.  Measurements:  Length  of  body,  1.60  mm.;  width  of  body,  0.81  mm.;  an- 
tenna, joint  I,  0.06  mm.;  joint  II,  0.04  mm.;  joint  III,  0.22  mm.;  joint  IV,  0.125 
mm.;  joint  V,  0.109  mm.;  joint  VI,  0. 081  mm.;  filament,  0.023  mm.  Cornicles,  0.06 
mm.  Cauda,  0.085  mm. 

Described  from  specimens  collected  in  the  fall  of  1911  at  San 
Jose,  Cal. 

THE   FULL-GROWN   MALE   PUPA. 

In  its  immature  stages  the  male  pupa  resembles  the  oviparous 
female.  A  description  of  a  single  full-grown  male  pupa  taken  at 
San  Jose,  Cal.,  October  27,  1912,  is  as  follows: 

General  color  pale  lemon  yellow.  Antennae  pale,  whitish,  i caching  to  the  anterior 
margin  of  the  metathorax;  last  three  joints  black  or  dusky.  Head  and  prothorax 
brownish.  Eyes  bright  red.  Wing  pads  very  pale.  Legs  entirely  whitish,  only  the 
hind  femora  bearing  the  characteristic  knee  spot;  tarsi  dusky  gray.  Cornicles  as 
broad  as  long.  Cauda  very  small,  rounded.  Cornicles  and  cauda  pale  yellow.  Head, 
thorax,  and  abdomen  with  two  longitudinal  dorsal  rows  of  oval  black  spots  and  with 
two  such  lateral  rows  of  circular  black  spots.  On  each  of  these  spots  is  situated  a  tuber- 
cle having  a  single  capitate  hair.  Excluding  the  wing  pads  the  body  resembles  that 
of  the  immature  sexual  female.  Measurements:  Length  of  body,  1.01  mm.;  width 
of  body,  0.50  mm.;  antenna,  joint  I,  0.049  mm.;  joint  II,  0.035  mm.;  joint  III, 
0.121  mm.;  joint  IV,  0.081  mm.;  joint  V,  0.087  mm.;  joint  VI,  0.063  mm.;  filament, 
0.023  mm. 

THE   WINGED  MALE,    ADULT  STAGE   (FIG.   8). 

General  color  of  the  body  pale  yellow  or  greenish  yellow.  Head,  prothorax,  and 
thorax  grayish  black.  Scutellum  black.  Eyes  bright  red.  Antennae  not  on  frontal 
tubercles,  reaching  to  the  posterior  margin  of  the  first  abdominal  segment,  pale  yellow; 
joints  I  and  II,  the  filament  or  spur,  and  the  articulations  of  joints  III  to  VI  dusky 
gray.  These  dark  articular  annulations  are  less  pronounced  than  in  the  viviparous 
female.  Wings  of  medium  size;  costa,  subcosta,  and  insertions  pale  yellowish  gray; 
stigma  short  and  gray,  with  its  central  area  paler;  veins  gray,  second  fork  of  third 
discoidal  nearer  to  the  wing  apex  than  to  the  first  fork  and  arising  beyond  the  apex 
of  the  stigmatic  vein;  stigmatic  vein  evenly  and  gently  curved,  absent  in  the  middle 
for  a  space  equal  to  one-third  of  its  length.  Legs  longer  in  proportion  to  the  body  than 
those  of  the  other  forms;  front  legs  and  middle  tibiae  very  pale  yellow  or  yellowish 
green;  distal  two- thirds  of  the  middle  and  hind  femora  shaded  gray,  the  black  knee 
spot  being  present  on  these  four  femora;  hind  tibiae  shaded  gr&y  for  its  proximal  three- 
fourths,  its  apical  fourth  pale  yellow;  all  tarsi  light  gray.  Abdomen  barely  as  long 
as  the  head  and  thorax  combined,  widest  at  the  fourth  segment,  and  with  a  pair  of 


Bui.  100,  U.  S.  Dept.  of  Agricultu 


PLATE  II. 


EGGS  OF  EUROPEAN  WALNUT  APHIS  (CHROMAPHIS  JUGLANDICOLA)  ON 
PIECE  OF  BARK  OF  EUROPEAN  SEEDLING  WALNUT.  TWICE  NATURAL 
SIZE. 


WALNUT  APHIDES  IN   CALIFORNIA. 


17 


oval  gray  transverse  spots  on  the  fifth  segment,  which  are  separated  by  a  space  equal 
to  their  length.  Cornicles  pale  yellow,  about  as  broad  at  the  base  as  long,  very  much 
as  in  the  winged  female.  Cauda  pale  yellow,  globular,  not  quite  as  long  as  the  hind 
tarsus.  Sexual  organ  pale  yellow.  Beak  pale  yellow,  slightly  exceeding  the  fore 
coxse.  Sterna  black.  Sensoria  transversely  oval,  situated  in  an  irregular  row  aa 
follows;  joint  III,  11  to  16;  joint  IV,  5  to  7;  joint  V,  4  to  5;  joint  VI,  2  besides  usual 
terminal. 

Measurements:  Length  of  body  (average),  1.47  mm.;  width  of  body  (maximum), 
Q.48  mm.;  expanse  of  wings  (average),  4.20  mm;  antenna,  joint  I,  0.05  mm.;  joint  II, 
0.04  mm.;  joint  III,  0.34  mm.;  joint  IV,  0.12  mm.;  joint  V,  0.12  mm.;  joint  VI,  0.08 
mm. ;  filament,  0.03  mm. ;  cornicles,  0.05  mm. 


a-pMs  juglandicola:  Winged  male  (appendages  of  left  side  removed),    a,  Left  antenna. 
(Original.) 

Described  from  many  individuals  collected  in  1911  and  V12  at 
San  Jose,  Cal. 

Both  the  male  and  the  winged  viviparous  female  .nen  disturbed 
have  a  habit  if  jumping  psyllid-like  into  the  air.  Their  flight  is 
generally  in  the  form  of  a  long  spiral,  and  when  disturbed  they  fly  in 
an  upward  direction. 

EGG    DEPOSITION. 

As  mentioned  before,  the  first  sexual  females  of  the  year  remain 
longer  on  the  leaves  after  they  have  reached  the  adult  state  than 
those  developing  later.  In  1911  eggs  were  not  observed  in  the 
field  until  September,  or  seven  weeks  after  the  first  appearance  of 
sexual  females.  In  1912  some  eggs  appeared  in  August.  This  long 
period  between  the  first  appearance  of  the  sexed  females  and  the 
40859°— Bull.  100—14 3 


18  BULLETIN   100,   U.    S.   DEPARTMENT   OF   AGRICULTURE. 

earliest  egg  deposition  may  be  explained  by  the  fact  that  until  late 
in  August  males  are  quite  scarce  and  so  the  females  must  wait  on 
the  leaves  until  the  males  are  developed.  Directly  after  mating  the 
female  repairs  to  the  branches  and  limbs  to  deposit  her  eggs.  Al- 
though eggs  may  be  deposited  anywhere  along  the  limbs,  and  more 
rarely  on  the  newer  growth,  the  locations  most  preferred  are  the  old 
scars  of  fallen  leaves  and  the  surface  of  the  larger  limbs  near  their 
bases.  Another  favored  location  is  that  in  the  crotches  of  the  smaller 
limbs.  Eggs  are  rarely  laid  along  the  stalk  of  the  leaf  or  at  the  base 
of  the  leaflets,  and  if  placed  in  those  positions  they  fall  to  the  ground 
when  the  leaf  drops.  Cavities  and  interstices  in  the  bark  are  also 
chosen,  but  when  infestation  is  very  severe  the  eggs  are  laid  in  the 
open  on  the  larger  limbs  (see  PL  II).  In  such  a  case  large  groups  of 
eggs  are  massed  together  by  many  females,  but  a  single  female  lays  not 
more  than  three  or  four  in  a  group.  The  eggs  are  fastened  together 
and  to  the  plant  surface  by  a  thin,  transparent,  gluey  substance.  No 
accurate  information  was  obtained  as  to  the  number  of  eggs  a  single 
aphis  produced,  but  from  general  field  observations  together  with 
dissections  of  gravid  females  the  writer  arrived  at  the  conclusion  that 
not  more  than  30  eggs  fell  to  the  share  of  each  adult,  and  probably 
not  over  half  that  number.  On  July  20,  1911,  five  gravid  females 
were  dissected.  These  contained  respectively  5,  3,  3,  4,  and  4  well- 
developed  ova,  besides  about  a  dozen  much  smaller  ones.  On  August 
28,  1912,  four  oviparous  females  dissected  contained  respectively 
2,  2,  4,  and  2  full-grown  ova  besides  about  20  much  smaller  ones.  All 
these  individuals  were  taken  on  the  leaves  and  had  not  oviposited. 
The  largest  eggs  dissected  were  lozenge-shaped  and  measured  0.37 
mm.  in  length  by  0.14  mm.  in  width. 

THE  EGG  (FIG.  l;  PL.  n). 

When  first  laid,  the  egg  is  pale  lemon-yellow  or  whitish  yellow,  oval, 
almost  twice  as  long  as  broad,  flatter  than  most  eggs  of  Aphidida?, 
and  slightly  broader  at  the  micropylar  end.  After  two  or  three  days 
it  turns  black  and  shines  obscurely  when  placed  under  a  strong  light. 
The  surface  is  beautifully  sculptured  with  granular  hexagonal  mark- 
ings. These  markings  arc  thickened  portions  of  the  shell.  The  nar- 
row intermediate  portions  of  the  shell  are  extremely  thin,  so  much  so 
that  four  months  after  the  egg  has  been  laid  the  yellow  interior  sub- 
stance is  plainly  visible  through  them  if  subjected  to  a  high  power  of 
magnification.  It  appears  that  about  85  per  cent  of  the  eggs  are 
fertile.  The  average  size  is  0.50  mm.  by  0.28  mm.  The  egg  stage 
may  be  said  to  occupy,  on  the  average,  five  months  in  California. 


WALNUT   APHIDES   IN    CALIFORNIA.  19 

ANT  ATTENDANTS. 

The  sweet  juices  excreted  by  the  European  walnut  aphis  attract 
large  numbers  of  ants,  of  which  a  large  black  species,  Formica  sub- 
sericea  Say,  is  the  most  abundant.  The  author  is  indebted  to  Mr. 
Theo.  Pergande,  of  the  Bureau  of  Entomology,  Washington,  D.  C., 
for  the  determination  of  this  species. 

THE  AMERICAN  WALNUT  APHIS  (Monellia  caryae  Monell).1 

Callipterus2  caryae  Monell,  U.  S.  Geol.  &  Geog.  Survey  Bui.  5,  No.  1,  p.  31,  Jan.  22, 
1879. 

Monellia3  caryae  Gillette,  Jour.  Econ.  Ent.,  v.  3,  No.  4,  p.  367,  fig.  6,  Aug.,  1910. 

HISTORY  OF  THE  SPECIES. 

This  plant-louse  was  first  collected  in  Missouri  by  Mr.  J.  T.  Monell 
in  1879.  His  original  description  is  as  follows: 

Winged  form;  general  color  pale  yellow;  tips  of  antennal  joints  black;  legs  entirely 
pale  whitish.  Antennae  a  little  shorter  than  the  body;  seventh  joint  equal  to  or 
one-third  longer  than  the  preceding;  fifth  joint  as  long  as  the  two  following  taken 
together.  Nectaries  not  perceptible.  Rostrum  not  reaching  to  the  middle  coxae. 
Wings  hyaline,  veins  pale;  stigma  rather  short  and  blunt  at  the  apex.  Stigmal  vein 
subobsolete,  its  course  being  only  traced  with  difficulty.  The  distance  between  the 
apex  of  the  lower  cubital  branch  and  that  of  the  second  discoidal  equal  to  about 
one-half  the  distance  between  the  apices  of  the  first  and  second  discoidals.  Apterous 
viviparous  females  and  pupge  with  four  rows  of  tubercles,  each  mounted  with  a  capitate 
bristle. 

Leaves  of  walnut,  hickory  and  pecan.     June-July,  St.  Louis,  Mo. 

This  aphis  has  been  reported  from  Illinois  (Thomas,  1880;  Davis, 
1910),  Nebraska  (Williams,  1910),  Oregon  (GiUette,  1910),  and 
Michigan  (Gillette,  1910),  and  doubtless  occurs  in  America  wherever 
its  food  plants  grow. 

GENERAL  DESCRIPTION;  CHARACTER  AND  EXTENT  OF  INJURY. 

This  aphis  is  about  one-sixteenth  of  an  inch  long  and  about  one- 
third  as  wide  and  is  generally  of  a  pale  lemon-yellow  color.  It 
occurs  on  the  lower  surface  of  the  leaf  and  on  the  nutlets  of  the 
eastern  black  walnut  tree  and  crosses  derived  from  it.  When  infes- 
tation is  severe,  the  aphides  will  also  be  found  on  the  upper  surface 
of  the  leaves.  The  species,  according  to  Mr.  Monell  and  other 
writers,  feeds  also  on  hickories  and  pecan.  The  character  and  extent 
of  its  injury  is  altogether  similar  to  that  of  the  European  walnut 
aphis  (ChromapTiis  juglandicola  Kalt.).  This  plant-louse  does  not  lie 
so  flatly  appressed  to  the  plant  surface  as  the  European  species  and 
is  much  more  active,  bearing  longer  legs  and  antennae  in  proportion 

1  Mr.  J.  T.  Monell,  of  the  Bureau  of  Entomology,  has  kindly  identified  the  specimens  sent  to  him  by  the 
author  as  Monellia  caryae  Monell. 

2  The  genus  Callipterus  ("beautiful-winged")  was  erected  by  Koch  (1855). 

3  The  genus  Monellia  was  erected  by  Oestlund  (1887),  with  caryella  Fitch  as  the  type  species. 


20 


BULLETIN   100,    U.    S.    DEPARTMENT   OF    AGRICULTUEE. 


to  the  size  of  the  body.  When  on.  the  lower  surface  of  the  leaflet  it  has 
the  habit  of  resting  with  the  head  directed  straight  toward  the 
peduncle  of  the  leaflet.  In  July  and  August,  in  which  months  this 
insect  is  most  abundant,  as  many  as  400  individuals  may  be  found  on 
one  leaflet,  5  per  cent  of  which  will  be  resting  on  the  upper  side.  At 
this  time  it  is  much  sought  after  by  ants,  which  feed  on  the  liquid 
excreted  by  it.  A  large  red  and  black  species,  determined  by  Mr. 
Theodore  Pergande  as  Formica  obscuriventris  Mayr,  is  a  very  common 
attendant.  Formica  subsericea  Say  also  attends  it.  The  sweet  excre- 
tions of  the  aphis  attract  many  flies  of  the  families  Muscidae,  Anthom- 
yiidae,  Oscinidae,  and  Syrphidae,  many  large  bees  including  the 
honeybee,  wasps  of  the  family  Pompilidse,  and  parasitic  wasps  of  the 
families  Ichneumonidse  and  Braconidae,  and  numerous  smaller  forms 
of  insect  life.  The  author  first  observed  this  aphis  on  July  20,  1911, 
at  San  Jose,  Cal. 

LIFE  HISTORY  AND  TECHNICAL  DESCRIPTIONS. 

THE  VIVIPAROUS  OR  ASEXUAL  FORMS. 

The  stem-mothers  hatch  as  soon  as  the  buds  start  to  swell,  about 
the  1st  of  April.  These  develop  into  winged  aphides  and  pass  their 
life  cycle  in  from  25  to  30  days,  according  to  temperature  and  the 
amount  of  food  supply.  The  viviparous  aphis  passes  through  four 
molts,  becoming  winged  after  the  final  one.  Table  VII  indicates  the 
life  cycle  of  38  individuals  of  the  summer  generations. 

TABLE  VII. — Life-cycle  of  viviparous  females  of  Monellia  caryae,  summer  generations, 
San  Jose,  Cal,  1912. 


No.  of  indi- 
vidual. 

Gener- 
ation. 

Date  of 
deposi- 
tion. 

Date  of 
acquiring 
wings. 

Life 
cycle. 

No.  of  indi- 
vidual. 

Gener- 
ation. 

Date  of 
deposi- 
tion. 

Date  of 
reaching 
maturity. 

Life 
cycle. 

1  
2  

II 
II 

Apr.  22 
22 

May   12 
12 

Days. 
£ 

%  

V 
V 

June  22 
23 

July     7 

Da% 

14 

3  
4  
5  

6  
7  
8  
9 

II 
II 
II 
II 
II 
III 
III 

22 

1 
1 
13 
13 

12 
20 
22 

23 
29 
29 

20 
19 
21 
22 
22 
16 
16 

22  
23  
24  
25  
26  
27  
28 

V 

v 

V 

V 

V 

v 
v 

23 
24 

24 
24 
24 
24 
24 

7 
7 
7 
7 
8 
8 
g 

14 
13 
13 
13 
14 
14 

10  
11  
12  

III 
III 
III 

13 
13 
13 

29 
29 

29 

16 
16 
16 

29.   ... 
30.   ... 
31.   ... 

V 

v 
v 

25 
25 
25 

8 
8 
8 

13 
13 
13 

13  
14  

15 

III 
III 
III 

13 
13 
13 

30 
30 
30 

17 
17 
17 

32.   ... 
33.   ... 
34 

V 

v 
v 

25 
25 

27 

8 
9 
10 

13 
14 
13 

16  
17  
18  

19 

III 
III 
V 
V 

13 
13 
June  22 
22 

30 
30 
July     4 

17 
17 
12 
15 

si:  ::: 

36.   ... 
37.   ... 
38 

V 
V 

v 

VI 

27 
27 

27 
July   13 

10 
10 
10 
Aug     1 

13 
13 

13 
19 

Thus,  the  second  generation  requires  20  days,  the  third  16  or  17, 
and  the  fifth  15,  in  which  to  complete  the  life  cycle.  Kecords  of  the 
fourth  generation  were  not  obtained  owing  to  premature  death  of  all 


WALNUT   APHIDES   IN    CALIFORNIA. 


21 


individuals  of  this  generation  of  which  the  date  of  deposition  had 
been  ascertained.  Individuals  of  the  fourth  generation  probably 
mature  in  an  average  of  16  days.  The  leaves  of  the  Eastern  black 
walnut  fall  earlier  than  those  of  the  European  or  California  black 
types,  and  consequently  the  viviparous  aphides  are  not  found  so  late 
on  the  trees.  There  are  probably  not  more  than  nine  generations  of 
these  in  a  year. 

Immediately  after  passing  the  final  molt  the  aphides  begin  depos- 
iting young.  These  are  entirely  pale  lemon-yellow  with  red  eyes 
and  four  longitudinal  rows  of  capitate  hairs  and  do  not  exceed  0.70 
mm.  in  length.  From  10  to  20  young  are  produced  by  a  single  female, 
dependent  on  the  season  of  the  year.  The  earlier  generations  are 
more  prolific.  After  midsummer  the  progeny  becomes  smaller  and 
smaller  with  successive  broods. 

THE    PUPA    OP   THE    WINGED    VIVIPAROUS   FEMALE    (FIG.  9). 

After  the  second  molt  the  pupal  wing  pads  are  apparent  as  small 
emarginations  on  the  sides  of 
the  thorax,  but  after  the  fol- 
lowing molt  they  are  much 
more  readily  seen.  The  pupa 
of  the  winged  viviparous  female 
may  be  described  as  follows  : 

Color  generally  pale  lemon-yellow, 
sometimes  white;  head  often  with  a 
reddish  tinge.  Antennae  on  small 
frontal  tubercles,  pale  yellow,  with 
the  filament  and  articulations  of  joints 
3  to  6  dusky  black.  Eyes  bright  red. 
Thoracic  segments  and  wing  pads 
light  yellow,  wing  pads  projecting 
out  from  the  body  at  a  very  acute 
angle.  Legs  pale,  tarsal  apices  dusky. 
Body  beset  with  long  capitate  spines 

in  four  rows.     Cornicles  on  segment  6 

0      ..  . 
of  the  abdomen,  hardly  perceptible, 

broader  than  long.  Cauda  blunt, 
conical,  and  short.  Cornicles  and  cauda  concolorous  with  the  abdomen.  Beak 
pale,  reaching  to  the  middle  coxse.  Measurements:  Length  of  body  (average),  1.87 
mm.;  width  of  body  (average),  0.71  mm.;  antenna,  joint  I,  0.058  mm.;  joint  II,  0.050 
mm.;  joint  III,  0.287  mm.;  joint  IV,  0.207  mm.;  joint  V,  0.201  mm.;  joint  VI,  0.128 
mm.;  filament,  0.136  mm. 

This  pupa  is  distinguishable  from  that  of  Chromaphis  by  the  pres- 
ence of  the  dorsal  rows  of  spines  and  by  the  absence  of  the  black 
femoral  spots.  The  penultimate  instar  occupies  on  the  average  four 
or  five  days.  At  its  termination  the  final  molt  occurs,  and  after  this 
the  insect  has  acquired  its  full  development. 


FIG.  Q.—Monettia   caryx:  Pupa   of   winged    viviparous 
female    (Originai.) 


22 


BULLETIN   100,    U.    S.    DEPAETMENT   OF    AGBICULTURE. 


THE    WINGED   VIVIPAROUS   FEMALE    (FIG.  10). 

General  color  pale  lemon-yellow;  many  examples  are  greenish  yellow  and  others 
decidedly  pinkish.  Head,  thoracic  lobes,  and  scutellum  pale  brown  or  yellowish 
brown.  Eyes  pink.  Antennae  on  small  frontal  tubercles,  about  half  as  long  as  the 
body,  pale  yellow,  with  articulations  of  joints  III  to  VI  black;  joint  III  the  longest, 
not  noticeably  thickened  basally;  joint  IV  slightly  longer  than  V  and  barely  as  long 
as  joint  VI,  together  with  its  spur  or  filament.  Bases  of  antennas  encircled,  in  the 
majority  of  individuals,  with  a  narrow  dusky  ring.  Close  to  the  lateral  margins  of 
the  prothorax  and  roughly  parallel  to  them  occur  two  narrow  black  lines.  (These  are 
sometimes  absent.)  Wings  of  moderate  size;  costa,  subcosta,  and  stigma  pale  yellow- 
ish green,  other  veins  light  brown,  of  medium  thickness.  Stigmatic  vein  entirely 
subobsolete,  its  course  not  easily  made  out.  Legs  very  pale,  whitish,  tarsi  and  apex 


FIG.  10.—  Mondlia  caryx:  Winged  viviparous  female,    a,  Antenna.    (Original.) 

of  tibiae  dusky  grey;  anterior  and  posterior  femora  in  about  half  of  the  individuals 
bear  a  grey  knee  spot  quite  like  that  of  Chromaphis  juglandicola  Kalt.  but  smaller. 
This  spot  never  occurs  on  the  middle  femora.  Abdomen  pale  yellow,  sometimes 
greenish  and  at  other  times  reddish,  with  four  rows  of  small  black  spots,  which  are 
very  variable  and  often  wholly  absent.  The  two  lateral  rows  have  larger  spots  and 
these  are  found  on  segments  2-6;  the  two  median  rows  are  smaller  and  their  spots 
exist  on  segments  2-8.  Cornicles  on  segment  6,  hardly  perceptible,  more  than  twice 
as  broad  as  long,  about  0.008  mm.  long.  Cauda  globulaV,  shorter  than  the  hind  tarsus. 
Cornicles  and  cauda  concolorous  with  the  abdomen.  Anal  plate  bifid,  armed  with 
spines.  Beak  pale,  extreme  tip  brown  and  not  quite  extending  to  the  second  pair  of 
coxse.  Sensoria  occur  on  the  antennae  as  follows:  Joint  III,  6-9  transversely  oval  on 
basal  half  or  two-thirds  of  joint;  in  an  equally  spaced  row;  joint  V,  1  terminal;  joint  VI, 
4  terminal  (1  large,  3  small).  Measurements:  Length  of  body,  2.16  mm.;  width  of 


WALNUT   APHIDES   IN    CALIFORNIA.  23 

body,  0.754  mm.;  wing  expanse,  4.44  mm.  Antenna,  joint  I,  0.076  mm.;  joint  II 
0.060  mm. ;  joint  III,  0.416  mm. ;  joint  IV,  0.273  mm. ;  joint  V,  0.273  mm. ;  joint  VI, 
0.143  mm.;  filament,  0.164  mm. 

Described  from  many  specimens  taken  at  San  Jose,  Cal.,  during 
1911  and  1912. 

The  complete  absence  of  the  stigmatic  vein  and  the  relatively 
longer  antennae,  together  with  the  diminutive  cornicles,  will  readily 
distinguish  this  species  from  the  European  walnut  aphid. 

In  18  months'  study  of  this  plant-louse  the  author  has  failed  to 
find  any  trace  of  the  existence  of  a  wingless  viviparous  form. 

THE  OVIPAROUS  OR  SEXUAL  FORMS. 

If  a  tree  be  heavily  infested,  the  sexual  forms  appear  first  about  the 
middle  of  July  and  probably  belong  to  the  fifth  and  sixth  generations. 
If  infestation  be  only  moderate  or  slight,  these  forms  are  not  pro- 
duced until  several  weeks  later  and  will  be  members  of  the  seventh 
and  following  generations.  The  sexed  forms  from  the  beginning  are 
produced  in  comparative  abundance  and  comprise  from  30  to  50 
per  cent  of  the  whole.  The  young  sexed  females  are  paler  and  more 
spindle-shaped  than  the  young  of  the  viviparous  individuals,  while 
the  male  larvss  and  pupae  are  conspicuously  brick-red  in  color.  The 
male  is  not  so  greatly  outnumbered  by  the  female  as  in  the  European 
walnut  aphis,  and  from  the  first  comprises  from  20  to  30  per  cent  of 
the  sexed  insects.  On  August  26  and  27  and  September  5,  1912,  a 
count  of  the  forms  on  34  leaflets  taken  at  random  from  an  Eastern 
black  walnut  tree  showed  177  viviparous  females,  14  males,  and  26 
sexed  females.  Probably  as  many  again  of  the  sexed  females  in 
proportion  to  the  leaflets  counted  could  be  found  on  the  twigs 
ovipositing.  Copulation  takes  place  on  the  leaf  and  occupies  half  a 
minute.  All  through  August  and  September,  1912,  the  oviparous 
females  were  observed  on  the  twigs,  but  few  eggs  were  found  until 
September.  After  the  middle  of  September  few  aphides  were  found, 
the  great  majority  having  been  destroyed  by  their  natural  enemies, 
but  those  that  escape  perpetuate  the  species  until  the  leaves  fall  in 
November.  The  majority  of  aphides  born  in  the  late  fall  are  sexual. 
The  sexed  female  shortly  after  mating  becomes  much  swollen  by 
reason  of  the  growing  ova  in  her  body,  and  the  last  four  abdominal 
segments  become  orange  colored.  She  repairs  to  the  twigs  and  limbs 
and  wanders  around  searching  for  locations  wherein  to  oviposit. 
Occasionally  immature  females  wander  off  to  the  twigs,  but  later 
return  to  the  leaves  to  resume  feeding.  The  fully  mature  fertilized 
oviparous  female  once  she  has  forsaken  the  leaf  rarely  if  ever  returns, 
and  thus  escapes  many  predatory  foes.  Having  found  a  crevice  or 
crack  in  the  cortex  suitable  for  her  purpose  she  grips  the  limb  with 


24 


BULLETIN   100,    U.    S.    DEPARTMENT   OF   AGKICULTUEE. 


her  six  legs  and  bends  the  hind  part  of  the  abdomen  at  a  right  angle 
to  the  rest  of  the  body  and  then  gives  her  abdomen  a  succession  of 
jerks  to  get  it  into  place.  This  performed  to  her  satisfaction,  she 
remains  motionless  for  60  seconds  while  the  egg  is  being  extruded,  and 
after  depositing  it  walks  off.  The  writer  has  never  seen  the  eggs  of 
this  species  placed  in  an  open  situation,  but  always  in  some  protected 
position  in  the  bark.  On  August  28,  1912,  four  gravid  females  were 
dissected  and  were  found  to  contain  respectively  3,  4,  2,  and  4  large 
eggs,  and  all  had  several  smaller  ones.  Another  had  8  large  eggs  in 
her  ovaries  and  was  greatly  distended  therefrom.  The  egg  is  bluntly 
oval,  bright  yellow  when  first  laid,  but  changing  in  a  day  or  two  to 
black  and  obscurely  shining.  It  measures  0.35  mm.  in  length  and 
0.17  mm.  in  width,  and  is  therefore  considerably  smaller  than  the 

egg  of  the  European  walnut  plant-louse. 

The  oviparous  forms  are  described  below. 

THE   OVIPAROUS  FEMALE,   FULL   GROWN  (FIG.   11 ). 

General  color  pale  greenish  yellow  or  sometimes 
greenish  white,  the  four  apical  segments  of  the 
abdomen  at  first  colored  like  the  rest  of  the  body 
and  later  orange  colored.  Body  rather  narrow, 
not  at  all  flattened,  the  sides  nearly  parallel  and 
produced  posteriorly  into  a  conical  tube.  An- 
tennae a  little  over  one-half  the  body  in  length, 
pale,  with  the  apical  third  or  fourth  of  joints  III 
to  VI  dusky  gray;  joint  II  gray  and  armed  with 
a  capitate  spine  on  its  inner  margin;  joint  III 
longest;  joints  IV  and  V  subequal;  joint  VI 
shorter  than  its  spur  or  filament.  Legs  very  pale 
yellow,  with  a  dark  spot  close  to  the  apex  of  the 
anterior  and  posterior  femora.  (In  many  individ- 
uals these  spots  are  absent.)  Eyes  pink.  The 
arrangement  of  capitate  spines  is  as  follows:  The  head  bears  eight,  the  prothorax 
six,  the  mesothorax,  metathorax,  and  abdominal  segments  1  to  5,  inclusive, 
four,  and  abdominal  segments  6,  7,  and  8  two;  these  spines  appear  as  four  lon- 
gitudinal rows.  Cornicles  greenish  yellow,  broader  than  long,  hardly  percep- 
tible, located  on  segment  6.  Cauda  concolorous  with  the  body,  globular,  armed 
with  four  noncapitate  spines,  half  as  long  as  the  hind  tarsus.  Genital  plate  protrud- 
ing beyond  the  cauda,  pale,  its  margin  beset  with  short  noncapitate  hairs.  Beak 
pale,  its  extreme  tip  brownish,  just  exceeding  the  second  pair  of  coxae.  Measure- 
ments: Length  of  body,  1.68  mm.;  width  of  body,  0.72  mm.;  cauda,  0.038  mm.; 
antenna  joint  I,  0.04  mm.;  joint  II,  0.035  mm.;  joint  III,  0.300  mm.;  joint  IV, 
0.17  mm.;  joint  V,  0.17  mm.;  joint  VI,  0.100  mm.;  filament,  0.12  mm. 

Described  from  many  specimens  collected  at  San  Jose,  Cal.,  during 
1912. 


FIG.  11. — Monellia    caryx:    Oviparous 
female.    (Original.) 


WALNUT  APHIDES  IN   CALIFORNIA.  25 

YOUNG   MALE    PUPA. 

Light  red  in  general  color;  appressed  closely  to  the  leaf  surface.  Dorsum  of  head 
in  front  black,  behind  gray.  Dorsum  of  thorax  gray.  Antennae  six-jointed  (i.  e., 
with  five  joints  and  filament),  one-third  as  long  as  the  body,  pale  gray.  Eyes  bright 
red.  Legs  pale,  femora  dusky  gray.  Mesothorax,  metathorax,  and  first  five  abdominal 
segments  each  with  four  black  spots  in  a  transverse  row.  Abdominal  segments  6  to  8, 
inclusive,  with  two  such  spots.  A  single  capitate  spine  arises  from  each  of  these 
spots.  Cornicles  imperceptible.  Cauda  pale,  short,  conical.  Beak  pale,  tip  dusky 
gray,  reaching  first  coxae. 

FULL-GROWN    MALE    PUPA    (FIG.    12). 

General  color  t>ale  brick  red;  head  pale  orange.  Antennae  half  as  long  as  the  body, 
seven-jointed,  pale  yellow,  with  dusky  articulations.  Eyes  bright  red.  Legs  very 
pale,  femora  usually  slightly  dusky.  Wing  pads  white.  Whole  body  with  four 
longitudinal  rows  of  dark  capitate  spines  distributed  as  in  the  oviparous  female. 
Cornicles  on  segment  6,  appearing  as  little  rims  on  the  body  surface,  broader  than 
long,  concolorous  with  the  body.  Cauda  bluntly  conical,  very  short,  pale  yellow. 
Beak  pale  yellow,  extreme  tip  brown,  reaching  to  the 
first  pair  of  coxae.  Measurements:  Length  of  body, 
1.58mm.;  width  of  body,  0.57mm.;  cauda,  0.045mm. 
Antenna,  joint  I,  0.071  mm.;  joint  II,  0.054  mm.; 
joint  III,  0.257  mm.;  joint  IV,  0.173  mm.;  joint  Y, 
0.200  mm. ;  joint  VI,  0.12  mm. ;  filament,  0.12  mm. 

Described  from  several  specimens  col- 
lected at  San  Jose,  Gal.,  in  1912. 

WINGED   MALE    (FIGS.    13;   18,  a). 

General  color  pale  lemon-yellow  or  greenish  yellow ; 
head  and  a  median  quadrilateral  area  on  thorax  dark 
brown;  scutellum  dark  brown;  eyes  dark  red.  An- 
tennae not  mounted  on  frontal  tubercles,  about  as  long 

asthebody;  jomts  I  and  II  with  a  dusky  central  part;     ^  12__3Mfl  Malepupa> 

joints  III  to  VI  pale,  with  their  apices  dusky  gray;  (Original ) 

filament  pale;  joint  III  longest,  bearing  about  24 

small  oval  sensoria;  joints  IV  and  V  subequal,  both  bearing  10  to  15  small  sensoria 
arranged  along  the  outer  margin;  joint  VI  bearing  4  sensoria,  of  which  the  most 
distal  is  apical;  joint  VI  longer  than  the  filament,  the  two  together  scarcely  as 
long  as  joint  V.  Ocelli  distinct.  Wings  of  medium  size;  costa  and  insertions 
greenish  yellow;  stigma  short  and  moderately  broad,  dusky  gray,  with  a  large  paler 
central  area;  veins  brown,  the  third  discoidal  curving  considerably  to  meet  its 
second  fork;  second  fork  twice  as  near  to  the  first  fork  as  to  the  apex  of  the  wing; 
stigmatic  vein  obsolete  in  its  middle  portion.  Legs  longer  in  proportion  to  the  body 
than  in  the  winged  viviparous  female,  pale  greenish  yellow,  with  a  large  dusky  area 
near  the  apex  of  all  six  femora;  apices  of  tibiae  and  tarsi  dusky  gray.  Abdomen 
short,' not  quite  as  long  as  the  head  and  thorax  together,  widest  at  the  third  segment; 
segments  1  to  7,  inclusive,  with  two  lateral  black  spots,  one  on  each  side;  segments 
1  to  6,  inclusive,  and  segment  8  with  two  dorsal  black  spots,  one  on  either  side  of  the 
dorso-median  line;  the  lateral  spots  on  segments  1  to  6,  inclusive,  are  circular  or  sub- 
circular;  the  dorsal  pairs  on  these  segments  are  oval;  the  dorsal  spots  on  segments  6 
and  8  coalesce  narrowly  in  the  middle.  Cornicles  on  segment  6,  hardly  perceptible, 
broader  than  long.  Cauda  globular,  dusky,  half  as  long  as  the  hind  tarsus.  Repro- 


26 


BULLETIN    100,    U.    S.    DEPARTMENT   OF    AGRICULTURE. 


ductive  organ  white,  when  extended  about  as  long  as  antennal  joint  IV.  Beak  pale 
yellow,  extending  a  little  beyond  the  first  pair  of  coxae.  Sterna  and  apical  half  of 
the  underside  of  the  head  dark  brown.  Very  often  one  or  more  of  the  dusky  abdominal 
spots  are  absent.  Measurements:  Length  of  body,  1.39mm.;  width  of  body,  0.69mm.; 
wing  expanse,  4.10  mm.;  cauda,  0.049  mm.;  antennal  joint  I,  0.051  mm.;  joint  II, 
0.058  mm.;  joint  III,  0.362  mm.;  joint  IV,  0.238  mm.;  joint  V,  0.240  mm.;  joint 
VI,  0.114  mm.;  filament,  0.134  mm. 

Described  from  four  specimens  collected  at  San  Jose,  Cal.,  in  1912. 


FIG.  13. —  AfonfM/a  carya;.-  Winged  male,    a,  I^eft  antenna.    (Original.) 


THE  LITTLE  HICKORY  APHIS  (Monellia  caryella  Fitch). 

Aphis  caryella  Fitch,  [First]  Report  on  the  noxious,  beneficial,  and  other  insects 

of  the  State  of  New  York,  Albany,  p.  163-165,  1855. 
Callipterus  caryellus  Fitch,  Third  report  on  the  noxious  and  other  insects  of  the 

State  of  New  York,  Albany,  p.  448-449,  1856. 
Monellia  caryella,  Oestlund,  Geol.  &  Nat.  Hist.  Survey  Minn.  Bui.  4,  p.  45,  1887. 

HISTORY  OF  THE  SPECIES. 

The  little  hickory  aphis  was  first  collected  in  New  York  State  by 
Dr.  Asa  Fitch,  previous  to  the  year  1855.  The  following  is  Fitch's 
original  description: 

The  Little  Hickory  Aphis  (Aphis  caryella)  is  pale  yellow  with  white  antennae  which 
are  alternated  with  black  rings,  the  wings  are  transparent  and  without  spots,  their 
veins  slender  and  pale  yellow,  the  legs  yellowish  white  to  their  ends.  Length  0.12 
to  the  tips  of  the  •wings.  The  abdomen  is  depressed,  egg-shaped,  its  apex  slightly 


WALNUT  APHIDES  IN   CALIFORNIA.  27 

narrowed  and  elongated.  The  antennae  are  longer  than  the  body,  tapering,  seven- 
jointed;  two  basal  joints  as  broad  as  long,  twice  the  diameter  of  the  following  joints; 
third  joint  longest,  slightly  thicker  towards  its  base;  fourth  and  fifth  joints  rather  shorter 
than  the  third,  cylindric;  two  last  joints  together  about  equalling  the  fifth  in  length; 
the  sixth  swelled  at  its  tip  into  a  long  oval  knob,  the  seventh  more  slender  but  not 
capillary,  shorter  than  the  sixth ;  a  broad  black  band  at  the  base  of  the  third  and  each 
of  the  following  joints.  First  vein  of  the  fore  wings  straight  and  almost  transverse; 
second  vein  bent  near  its  base,  running  first  towards  the  apex  and  then  turning  rather 
abruptly  and  continuing  straight  to  the  inner  margin,  more  than  twice  as  far  from  the 
first  at  tip  as  base;  third  vein  arising  from  the  stigma  near  its  anterior  end,  and  not 
from  the  rib- vein  forward  of  the  stigma,  as  it  does  in  the  aphides  generally,  except 
those  pertaining  to  this  group,  its  base  and  its  apex  about  the  same  distance  from  the 
second  vein  that  this  is  from  the  first,  forking  rather  forward  of  its  middle,  strongly 
bent  at  this  point,  and  from  hence  to  its  i ip  parallel  with  the  third  vein  or  but  slightly 
diverging  from  it,  its  tip  a  third  nearer  that  of  the  third  vein  than  this  is  to  the  second; 
second  fork  nearer  the  fourth  vein  at  tip  than  to  the  first  fork,  the  triangular  cell  be- 
tween it  and  the  first  fork  with  its  three  sides  equal;  fourth  vein  short  and  often  nearly 
abortive,  shorter  than  the  second  fork,  equally  curved  through  its  whole  length,  its 
tip  much  nearer  that  of  the  rib-vein  than  that  of  the  second  fork;  rib- vein  very  slightly 
diverging  from  the  margin  from  the  base  to  the  stigma,  curved  from  thence  to  its  tip. 
Stigma  oval,  about  twice  as  long  as  wide,  watery,  sometimes  tinged  with  yellowish.  A 
variety  has  the  stigma  dusky  at  its  tip.  Another  variety  (costalis)  has  the  rib-vein 
coal  black  interrupted  with  whitish  towards  the  stigma,  which  is  dusky  and  black  at 
each  end. 

In  a  general  discussion  of  this  species  before  his  description  Fitch 
refers  to  the  minute  cornicles  characteristic  of  this  and  kindred 
species.  In  his  third  report  on  the  insects  of  New  York  he  mentions 
the  European  walnut  aphis  and  says  "European  C.  juglandicola  of 
Koch"  [ChromapMs  juglandicola  Kalt.]  " appears  closely  related  to 
this  present  species"  [i.  e.  Callipterus  caryellus].  Fitch  gave  the 
host  plant  of  his  species  as  the  hickory.  Oestlund  (1887)  reports  it 
^Minnesota  from  Carya  amara'Nutt.  Davis  (1910)  and  other  Eastern 
writers  record  it  from  hickory  in  the  Eastern  States.  In  California 
the  normal  food  plants  are  the  California  black  walnut  (Juglans 
calif ornica)  and  hybrids  derived  from  this  tree. 

GENERAL  APPEARANCE;  CHARACTER  AND  EXTENT  OF  INJURY. 

In  general  appearance  this  aphis  is  very  similar  to  the  American 
walnut  aphis  (Monellia  caryse  Monell)  and  can  not  be  distinguished 
from  it  except  when  viewed  under  the  microscope  or  a  powerful  hand 
magnifier.  Its  habits  of  life  and  the  character  and  extent  of  its 
injury  are  also  very  similar  to  those  of  M.  caryse.  The  writer  had 
observed  this  aphis  for  several  months  before  he  realized  that  it  was  a 
distinct  species  and  not  a  variety  of  caryse,  as  he  had  previously 
supposed.  When  the  sexed  forms  appeared  it  was  noticed  that  the 
oviparous  female  of  caryella  differed  markedly  from  the  same  form 
of  caryse,  and  this  led  to  a  closer  scrutiny  of  the  viviparous  form 
resulting  in  the  establishment  of  the  points  of  divergence  shown  in 
Table  VIII. 


28 


BULLETIN   100,    TJ.    S.    DEPARTMENT    OF    AGEICULTUEE. 


TABLE  VIII. — Divergences  of  structure  between  Monellia  caryse  Monell  and  M.  caryella 

Fitch. 


Form. 

Monellia  caryx  Monell. 

Monellia  caryella  Fitch. 

Winged  viviparous  female  

Pupa  of  viviparous  female  
Oviparous  female  

Antennal  joint  III  very  slightly 
thickened  basally. 
Sensoria  on  antennal  joint  III 
occupying  basal  half  or  two- 
thirds. 
Antennal  joint  VI  and  its  spur  or 
filament  subequal,  or  VI  less 
than  spur. 
Dusky  knee  spots  often  present. 
Four  longitudinal  rows  of  capitate 
spines. 
Smaller  than  the  viviparous  fe- 

Antennal joint  III  quite  notice- 
ably thickened  for  its  basal  half. 
Sensoria  on  antennal  joint  III  oc- 
cupying basal  third. 
Antennal  joint  VI  one-third  as 
long  again  as  its  spur  or  filament. 
Dusky  knee  spots  absent. 

Six  longitudinal  rows  of  capitate 
spines. 
Larger  than   the   viviparous   fe- 

male. 
Four  longitudinal  rows  of  capitate 
spines. 

male. 
Six  longitudinal  rows  of  capitate 
spines. 

LIFE  HISTORY  AND  TECHNICAL  DESCRIPTIONS. 

Life-history  studies  on  this  plant-louse  began  in  August,  1912,  at 
San  Jose,  Cal.,  but  no  rearing  work  was  done  until  the  appearance 
of  the  sexed  forms  in  September.  Observations  taken  in  August 
and  September  indicated  a  development  of  the  summer  generations 
similar  to  that  found  in  Monellia  caryse.  This  was  further  confirmed 
by  studies  during  1913.  The  sexed  forms  were  studied  at  Walnut 
Creek  and  San  Jose,  Cal.  In  both  localities  these  did  not  appear  until 
late  in  September,  even  on  trees  heavily  infested.  The  aphides  re- 
mained on  the  trees  as  long  as  there  were  leaves  on  which  they  could 
subsist  and  were  to  be  found  until  mid-November.  After  September 
the  great  majority  of  aphides  deposited  were  oviparous,  and  of  these 
the  males  were  extraordinarily  scarce,  the  writer  observing  only  one 
individual  of  this  sex  among  hundreds  of  oviparous  females.  Table 
IX  indicates  the  life  cycle  of  plant-lice  deposited  by  four  viviparous 
females  and  shows  the  preponderance  of  the  sexed  form  over  the 
asexual  in  the  late  fall. 

TABLE  IX. — Life-cycle  record  of  the  progeny  of  four  viviparous  females  of  Monellia 

caryella,  Walnut  Creek,  Cal.,  1912. 
FEMALE  NO.  1;  DEPOSITED  3  YOUNG. 


Date  of— 

No.  of  larva. 

Hatch- 
ing. 

Molt  1. 

Molt  2. 

Molt  3. 

Molt  4 
(beconi- 

adult). 

Form  of  individual. 

Life 
cycle. 

l 

Oct.     4 

Oct.      7 

Oct.    10 

(?) 

Oct.    If. 

Winged  viviparous  fe- 

*% 

male. 

2  

4 

7 

11 

(?) 

18 

Oviparous  female  

14 

31 

.do   .. 

FEMALE  NO.  2;  DEPOSITED  6  YOUNG. 


1 

Oct     12 

Oct     15 

Oct     18 

Oct.    21 

Oct.    28 

Oviparous  female  

16 

2  

12 

15 

18 

21 

28 

do  

16 

12 

15 

19 

22 
23 

29 
30 

....do  

do 

17 
18 

5 

12 

(?) 

(?) 

(?) 

29 

....do... 

17 

6 

12 

(?) 

(?) 

(?) 

30 

.do  

18 

i  Died  permaturely. 


WALNUT   APHIDES   IN    CALIFORNIA. 


29 


TABLE  IX. — Life-cycle  record  of  th> 
caryella,  Walnut 


ny  of  four  viviparous  females  of  Monellia 
*  '  ,  1912— Continued. 


FEMALE  NO.  3;  DEPOSITED  16  YOUNG. 


Date  of— 

No.  of  larva. 

Hatch- 
ing. 

Molt  1. 

Molt  2. 

Molt  3. 

Molt  4 
(becom- 
ing 
adult). 

Form  of  individual. 

Life 
cycle. 

Oct     16 

Oct     21' 

Oct     27 

Nov     3 

Days. 

2 

16 

21 

27 

3 

7 

do 

22 

3 

16 

21 

27 

3 

7 

do 

22 

4  

17 

(?) 

(?) 

(?) 

g 

do 

22 

5  

17 

? 

?) 

? 

do  

22 

6 

17 

\1 

?) 

(?) 

g 

do 

22 

7  

17 

? 

? 

(?) 

g 

do 

22 

8  

18 

? 

rj 

? 

g 

do  

21 

9  
101  

18 

? 

? 

(?) 

9 

do  

...  .do 

22 

Hi  

do 

12  > 

do 

131 

do 

141  

do 

15  i 

do 

161  

do. 

FEMALE  NO.  4;  DEPOSITED  g  YOUNG. 


1 

Oct     18 

Oct     22 

Oct     27 

Nov     2 

Nov 

Ovi  arous  female 

2... 

lg 

22 

27 

3 

9 

do 

22 

3 

18 

22 

27 

g 

do 

22 

4  

18 

22 

27 

4 

9 

do 

22 

51  

do 

9. 

do 

71 

do 

gi  

do 

Died  prematurely. 
SUMMARY. 


Life  cycle  (20  oviparous  females). 

Days. 

22 

Minimum  
Average  ... 

14 
18  92 

First  instar  (13  individuals),  average.  .  . 
Second  instar  (13  individuals),  average.. 
Third  instar  (11  individuals),  average... 
Fourth  instar  (11  individuals),  average  . 

3.7 
4.5 
5.7 
5.6 

The  viviparous  forms,  so  far  as  the  author  has  observed,  all 
develop  wings. 

The  eggs  of  this  aphis  are  larger  than  those  of  the  American  walnut 
aphis  and  measure  on  the  average  0.536  mm.  in  length  and  0.222  mm. 
in  maximum  width.  They  are  elongate-oval  in  shape,  rather  feebly 
shining,  and  have  a  softer  shell  than  is  found  in  the  eggs  of  the 
majority  of  plant-lice,  but  one  not  so  soft  as  is  that  of  (Jhromaphis 
juglandicola.  They  are  placed  either  singly  or  in  groups  of  two  or 
three  around  the  axils  of  the  buds  or  in  crevices  in  the  bark  and  in 
scars  caused  by  fallen  leaves  on  the  smaller  limbs  and  twigs.  Ovipo- 
sition  is  in.  progress  during  the  months  of  October  and  November,  each 
oviparous  female  laying  on  the  average  about  12  eggs.  Owing  to  the 


30  BULLETIN   100,   U.    S.   DEPARTMENT   OF   AGRICULTURE. 

scarcity  of  males  in  the  fall  of  1912  at  Walnut  Creek,  Cal.,  it  seemed 
very  probable  that  a  large  proportion  of  the  eggs  would  prove  to  be 
sterile,  and  in  the  following  spring  examinations  of  egg-infested  trees 
showed  this  assumption  to  be  correct. 

THE   VIVIPAROUS  FORMS. 

The  stem-mothers  commence  hatching  very  shortly  after  the  leaf 
buds  open  in  the  latter  part  of  March.  Previous  to  the  first  molt 
they  are  pale  lemon-yellow  with  red  eyes,  hyaline  legs,  and  dusky 
tarsi;  the  joints  of  the  antennae  have  black  articulations;  on  the 
abdomen  are  four  longitudinal  rows  of  circular  dusky  spots  from  each 
of  which  arises  a  capitate  spine.  They  are  destined  to  become  winged 
and  in  their  later  stages  do  not  differ  from  the  summer  winged 
viviparous  individuals. 


FIG.  14.—  Monellia  caryella:  Tupa  of  winged  viviparous  female.    (Original.) 
THE   PUPA   OP  THE   WINGED   VIVIPAROUS   FEMALE    (FIG.    14). 

General  color  pale  lemon-yellow;  some  individuals  exhibit  a  decided  greenish, 
others  a  decided  salmon  colored  tinge.  Antennae  two-thirds  of  the  body  in  length; 
apices  of  joints  III  to  VI  and  the  whole  filament  dusky,  otherwise  pale  yellow,  almost 
white.  Eyes  bright  red.  Head  with  eight  capitate  spines,  six  of  these  on  the  frontal 
margin  and  two  near  the  hind  border.  Prothorax  with  six  capitate  spines,  two  of 
these  near  the  middle  of  the  segment  and  four  in  a  transverse  row  along  the  hind 
margin.  Mesothorax,  metathorax,  and  abdomen  with  six  longitudinal  rows  of  capitate 
spines.  Legs  pale  yellow,  tarsi  dusky.  Wing  pads  pale,  after  being  imbedded  in 
balsam  for  a  few  days  becoming  dusky.  Cornicles  barely  perceptible,  wider  than 
long.  Cauda  rounded,  not  as  long  as  the  hind  tarsi  and  without  hairs.  Beak  pale 
with  a  brown  tip,  almost  reaching  the  second  pair  of  coxae.  Measurements:  Length 
of  body,  1.81  mm.;  width  of  body,  0.72  mm.;  antenna,  joint  I,  0.070  mm.;  joint  n, 
0.050  mm.;  joint  III,  0.253  mm.;  joint  IV,  0.198  mm.;  joint  V,  0.183  mm.;  joint  VI, 
0.134  mm.;  filament,  0.105  mm. 

Described  from  four  specimens,  Walnut  Creek,  Cal.,  October,  1912. 


WALNUT  APHIDES  IN   CALIFORNIA. 


31 


THE    WINGED    VIVIPAROUS    FEMALE    (FIG.    15). 

General  color  pale  lemon-yellow,  somewhat  varying  in  shade.  Antennae  about 
four-fifths  as  long  as  the  body,  pale  yellow,  with  joints  III  to  VI, inclusive,  bearing 
an  apical  black  ring  (on  joint  III  this  ring  is  narrower  than  the  other  joints);  fila- 
ment of  joint  VI  dusky;  joint  III  is  the  longest;  joints  IV  and  V  subequal  or  joint  IV 
slightly  longer  than  V;  joint  IV  about  four-fifths  as  long  as  III;  joint  VI  together  with 
its  filament  about  equal  to  V;  filament  about  three-fourths  as  long  as  VI;  basal  third 
of  joint  III  noticeably  swollen  and  bearing  from  five  to  seven  oval  transverse  eensoria; 
usual  apical  sensoria  on  both  joints  V  and  VI.  Head  pale  yellow,  with  the  frontal 
margin  black.  Eyes  bright  red.  Prothorax  pale  yellow,  with  two  narrow,  black, 
longitudinal  stripes  arising  from  the  anterior  angles  and  extending  for  two-thirds 


FIG.  15. — Monellia  caryetta:  Winged  viviparous  female,    a,  Right  antenna,  enlarged,  with  variations  of 
number  of  sensoria.    (Original.) 

of  its  width.  Thoracic  lobes  and  scutellum  light  brown,  sometimes  with  a  salmon- 
pink  tinge.  Wing  insertions,  costa,  subcosta,  and  stigma  pale  lemon-yellow;  dis- 
coidals  yellowish -brown;  first  and  second  discoidals  heavier  than  the  other  veins; 
third  discoidal  obsolete  at  its  immediate  base,  its  first  fork  equidistant  from  the 
second  fork  and  the  base  of  the  discoidal,  its  second  fork  nearer  to  the  first  fork  than 
to  the  apices  of  its  two  branches;  branches  of  second  fork  equal  in  length;  stigmatic 
vein  very  weak,  its  basal  half  traceable  only  with  difficulty;  lower  wing  colorless. 
Legs  pale  yellow;  tarsi  and  tibial  apices  dusky.  Abdomen  entirely  pale  lemon- 
yellow,  the  body  widest  at  the  third  segment.  Body  somewhat  narrowed  laterally. 
Cornicles  pale  yellow,  hardly  perceptible,  wider  than  long.  Cauda  globular,  bearing 
a  fringe  of  weak  hairs,  about  equal  in  length  to  the  hind  tarsi,  concolorous  with  the 
abdomen.  Genital  plates  armed  with  weak  hairs,  pale  yellow.  Beak  pale  yellow, 
its  extreme  tip  brown,  extending  halfway  between  first  and  second  coxae.  Measure- 


32 


BULLETIN   100,   U.    S.    DEPARTMENT   OF   AGRICULTURE. 


mente:  Length  of  body  (average),  1.67  mm.;  width  of  body  (average),  0.61  mm.; 
wing  expanse  (average),  4.02  mm.;  antenna,  joint  I,  0.053  mm.;  joint  II,  0.046  mm,; 
joint  III,  0.41  mm.;  joint  IV,  0.335  mm.;  joint  V,  0.32  mm.;  joint  VI,  0.191  mm.; 
filament,  0.123  mm.;  cauda,  0.084  mm.;  Cornicles,  0.009  mm. 

Described  from  numerous  specimens,  Walnut  Creek,  Cal.,  October, 
1912. 

THE  OVIPAROUS  FORMS. 

THE  OVIPAROUS  FEMALE  (FIG.  1C). 

Wingless.     General  color  pale  lemon-yellow,  in  mature  individuals  the  central  part 
of  the  abdomen  diffused  with  orange.     Body  elliptical,  "widest  at  the  third  abdominal 
jnt.     Antennae  half  as  long  as  the  body,  not  on  frontal  tubercles,  pale,  with 


FiQ.  16.—  Monellia  carydla:  Oviparous  female.     (Original.) 

an  apical  black  ring  on  joints  III  to  VI,  inclusive;  joints  I,' II,  and  filament  dusky; 
joint  III  longest;  joints  IV  and  V  subequal  and  each  about  four-fifths  as  long  as  joint 
III ;  filament  a  little  shorter  than  VI ;  VI  about  four-fifths  as  long  as  V.  Eyes  crimson. 
Legs  pale  yellow;  tarsi  dusky.  Hind  tibiae  slightly  thickened.  Cornicles  very 
small,  pale.  Cauda  pale,  globular,  beset  with  a  fringe  of  weak  hairs,  not  as  long  as 
the  hind  tarsi.  Thorax  and  abdomen  with  six  longitudinal  rows  of  capitate  bristles, 
each  surmounting  a  pale  tubercle.  Penultimate  segment  of  the  abdomen  encircled 
near  its  posterior  margin  with  a  fringe  of  weak  hairs.  Eight  capitate  spines  on  the 


WALNUT   APHIDES   IN    CALIFORNIA. 


33 


head  and  six  on  the  prothorax.  Tibia?  armed  with  a  row  of  short  bristles  on  their 
inner  margins.  Beak  pale,  the  extreme  tip  dusky,  extending  a  little  beyond  the 
anterior  coxae.  The  young  oviparous  female  is  entirely  pale  yellow  and  can  be  dis- 
tinguished from  the  young  viviparous  female  only  by  its  more  eliptical  shape,  that 
of  the  latter  being  more  oval.  Measurements:  Length  of  body,  1.89  mm.;  width  of 
body,  0.92  mm. ;  antenna,  joint  I,  0.075  mm. ;  joint  II,  0.042  mm. ;  joint  III,  0.312  mm. 
joint  IV,  0.203  mm.;  joint  V,  0.218  mm.;  joint  VI,  0.167  mm.;  filament,  0.108  mm. 
cauda,  0.080  mm.;  cornicles,  0.009  mm. 

Described  from  numerous  specimens,  Walnut  Creek,  Cal.,  October, 
1912. 

WINGED   MALE    (FIGS.    17;   18,  6). 

General  color  pale  green  or  greenish  yellow.     Head  and  prothorax  olive-green. 
Frontal  margin  of  head  and  frontal  margin  of  prothorax,  black.     Prothorax  with  two 


FIG.  l7.—  Monelliacaryella:  Winged  male.    (Original.) 

bluntly  rounded  dusky  tubercles  on  the  dorsum.  Dorsum  of  head  and  thorax  with 
indefinite  dusky  markings.  Eyes  red.  Antennae  dark  olive-green,  about  three- 
fourths  of  the  body  in  length;  joint  VI  longer  than  its  filament.  Sensoria  as  follows: 
III,about21:IV,7to9;V,6tolO;VI,2to4(besidestheusualapical).  Wings  of  mod- 
erate size;  insertions  and  subcosta  greenish-yellow;  stigma  light  brown,  with  a  paler 
central  area ;  discoidals  1  and  2  thicker  than  the  other  veins  and  with  a  narrow  smoky 
border;  stigma  tic  vein  obsolete  except  for  its  apical  third;  veins  brown.  Legs  pale 
greenish-yellow;  coxae,  trochanters,  apical  five-sixths  of  femora,  and  basal  four-fifths 
of  tibiae  black;  tarsi  gray.  Thoracic  lobes  and  scutellum  black.  Under  the  wings 


34 


BULLETIN   100,   U.    S.   DEPARTMENT   OF    AGRICULTURE. 


f- ; 


FIG.  18.— a,  Monettia  cargo:,  antenna  of  male; 
6,  Monettia  caryella,  two  views  of  right  an- 
tenna of  male.  (Original.) 


occurs  a  large  black  spot  on  the  pleurae. 
Abdomen  unarmed,  pale  green  or  green- 
ish yellow;  segments  1  to  8,  inclusive, 
with  two  dusky  brown  oval  spots  on 
each.  Cornicles  pale,  concolorous  with 
the  body,  very  small,  considerably 
broader  than  long.  Cauda  concolorous 
with  the  abdomen,  globular.  Abdomen 
about  as  long  as  head  and  thorax  com- 
bined, not  wider  than  the  thorax. 
Beak  pale,  barely  reaching  second 
coxse.  Sternum  and  underside  of  the 
eighth  abdominal  segment  black.' 

Measurements:  Length  of  body,  1.57 
mm.;  width  of  body,  0.62  mm.;  ex- 
panse of  wings,  4.62  mm.;  antenna, 
joint  I,  0.080mm.;  joint  II,  0.041  mm.; 
joint  III,  0.412  mm.;  joint  IV,  0.317 
mm.;  joint  V,  0.260  mm.;  joint  VI, 
0.175  mm.;  filament,  0.108mm.;  cauda, 
0.067  mm.;  cornicles,  0.009  mm. 

Described  from  three  speci- 
mens, Walnut  Creek,  Cal.,  1912 
and  1913. 

MONELLIA  CALIFORNICA  Essig. 

Monellia  californiais  Essig,  Pomona 
Jour.  Ent.,v.4,  no. 3,  p.  767,  Nov., 
1912. 

In  southern  California  feeding 
on  the  underside  of  the  leaves  of 
the  California  black  walnut 
(Juglans  californica)  there  has 
recently  been  found  a  plant- 
louse  closely  allied  to  MoneUia 
caryse  and  M.  caryella.  The 
writer  has  never  seen  this  aphis 
in  nature,  but  has  received  speci- 
mens from  Mr.  Essig,  who  de- 
scribed it. 

KEY  TO  THE  SPECIES  OF  MONEL- 
LIA KNOWN  TO  OCCUR  IN  CALI- 
FORNIA. 

The  following  key  will  serve 
to  distinguish  the  four  species 
of  walnut  aphides  occurring  in 
California. 


WALNUT   APHIDES   IN    CALIFORNIA.  35 

KEY  TO  THE  SPECIES  OF  APHIDID^E  KNOWN  TO  OCCUR  ON  WALNUT  IN  CALIFORNIA. 

A.  Cornicles  quite  evident,  about  as  wide  as  long. 

Chromaphis  juglandicola  Kalt. 

AA.  Cornicles  barely  perceptible,  considerably  wider  than  long. 
B.  Tibiae  of  winged  viviparous  female  entirely  dusky. 

Monellia  californica  Essig. 
BB.  Tibiae  of  winged  viviparous  female  for  the  most  part  pale. 

C.  Filament  of  joint  VI  longer  than  joint  VI ;  oviparous  female  with 

four  longitudinal  rows  of  capitate  hairs Monellia  can/at  Monell. 

CC.  Filament  of  joint  VI  shorter  than  joint  VI;  oviparous  female  with 
six  longitudinal  rows  of  capitate  hairs Monellia  caryella  Fitch. 

NATURAL  CONTROL  OF  WALNUT  APHIDES. 

INTERNAL  PARASITES. 

In  July,  1912,  a  small  chalcidid  wasp  was  observed  ovipositing  in 
a  pupa  of  Monellia  caryse.  This  is  the  only  record  of  parasitism  or 
attempted  parasitism  observed  during  two  seasons,  so  there  is  good 
reason  to  believe  that  these  aphides  are  practically  immune  from  the 
attacks  of  internal  parasites. 

FUNGOUS  DISEASES. 

Although  occasionally  a  plant-louse  may  be  noticed  here  and  there 
killed  by  fungus,  only  a  single  instance  of  the  destruction  of  a  colony 
by  this  agency  came  under  the  writer's  notice.  This  occurred  on 
May  20,  1911,  following  a  rainstorm,  and  all  the  plant-lice  on  a  few 
leaves  were  destroyed.  The  disease  did  not  spread  far,  some  cause 
or  other  checking  the  fungus  shortly  after  its  appearance. 

PREDACEOUS  ENEMIES. 

Predaceous  enemies  are  of  prime  importance  in  the  control  of 
plant-lice  on  walnuts  and  where  the  aphides  occur  hi  any  numbers 
may  always  be  found  preying  on  them  from  June  to  September. 
Unfortunately  they  do  not  make  their  appearance  on  the  walnuts 
until  their  prey  has  had  tune  to  do  much  damage  to  young  nuts  and 
to  become  abundant  enough  to  cause  collective  injury  to  the  tree. 
Should  these  predaceous  forms  appear  in  early  spring  they  would 
quickly  wipe  out  the  few  plant-lice  present  at  that  time  and  conse- 
quently their  progeny  would  starve  to  death.  As  injury  is  thus  done 
to  the  nuts  and  to  the  vitality  of  the  tree  before  the  advent  of  natural 
enemies,  artificial  measures  must  be  practiced  in  order  to  insure 
healthy  trees  and  perfect  nut  crops. 

The  predaceous  enemies  of  walnut  plant-lice  include  syrphus-fly 
larvae,  agromyzid  larvae,  chrysopid  and  hemerobid  larvae,  coccinellid 
beetles  and  their  larvae,  Camptobrochis  brevis  Uhler  (Heteroptera)  and 
its  larva,  and  various  spiders. 


36 


BULLETIN   100,    U.    S.    DEPARTMENT   OF    AGRICULTURE. 


SPIDERS. 

The  commonest  spider  predaceous  on  walnut  plant  lice  is  The- 
ridium  placens  Keyserling.  This  spider  may  be  found  on  the  trees 
during  the  months  of  August  and  September  and  has  a  habit 
of  curling  around  itself  the  edge  of  the  leaf  under  the  protec- 
tion of  which  to  deposit  its  egg  sac.  This  species  was  determined 
by  Mr.  Nathan  Banks,  of  the  Bureau  of  Entomology,  who  says  of  it 
"*  *  *  a  species  found  on  the  Pacific  coast.  They  do  not 
choose  their  food,  but  from  location  of  web  are  apt  to  get  many 
plant  lice."  This  and  other  spiders  are  of  comparatively  small 
economic  importance  in  the  control  of  aphides. 

CAMPTOBROCHIS  BKEVIS  UHLER. 

Camptobrochis  brevis  Uhler,  which  was  determined  by  Mr.  Otto 
Heidemann,  of  the  Bureau  of  Entomology,  is  a  small  black  capsid, 
measuring  in  the  adult  stage  4.2  by  1.9  mm.  Its  larva  is  white,  with 
conspicuous  black  markings.  Both  immature  and  mature  individ- 
uals were  observed  actively  and  abundantly  attacking  plant  lice 
during  August,  1912.  They  do  not  occur  in  numbers  earlier  in  the 
year  and  disappear  in  September.  Thus  their  beneficial  work  is 

limited. 

LEUCOPIS  sp. 

A  fly  of  the  family  Agromyzidse,  Leucopis  sp.,  in  ite  larval  state 
preys  upon  walnut  plant  lice  from  June  to  August.  The  small 
yellow  maggots  superficially  resemble  syrphid  larvae.  They  are 
never  very  abundant  and  are  not  a  great  factor  in  the  control  of  the 
"lice."  The  life  cycle  in  summer  is  completed  in  24  days  or  less 
and  there  are  several  broods  in  California. 

CHRYSOPID  OR  LACEWING  FLIES. 

Of  scarcely  less  importance  economically  than  the  ladybird  beetles 
and  syrphid  maggots  are  the  active  reddish-brown  larvae  of  the  "  lace- 
wings."  CJirysopa  majescula  Banks  and  C.  californica  Coq.  are  two 
species  of  economic  importance  in  California.  Table  X  shows  the 
predatory  activities  of  two  larvae  of  the  latter  species  in  the  fall  of 
1912.  The  aphides  consumed  by  these  larvae  were  of  all  sizes  and 
averaged  about  1.5  by  0.5  mm. 

TABLE  X. — Chrysopa  californica:  Predatory  activities  on   walnut  plant  lice,    Walnut 
Creek,  Cal.,  1912. 


Date  of— 

Number 

Larva 
No. 

Number 
"lice" 
eaten  to 
molt  1. 

Date  of 
molt  2. 

Number 
"lice" 
eaten, 
molt  1  to 
molt  2. 

Date  of 
spinning 
cocoon. 

"lice" 
eaten 
from 
molt  2 

toissr 

Total 
"lice" 
eaten. 

Num- 
ber 
days 
feed- 
ing. 

Hatch- 
ing. 

Moltl. 

1 

Sept.  18 

Sept.  22 

11 

Sept.  27 

70 

Oct.     8 

265 

346 

20 

2 

18 

21 

22 

26 

57 

7 

300 

379 

19 

WALNUT   APHIDES   IN    CALIFORNIA. 


37 


Larva  No.  1  ate  on  the  average  17.3  "lice"  per  day,  while  larva 
No.  2  consumed  19.9  "lice"  per  day.  The  lacewing  larvae  appear 
in  numbers  toward  the  end  of  June  and  may  be  found  until  the  end 
of  October.  There  are  probably  at  least  three  broods,  the  last  one 
wintering  in  the  cocoon,  which  is  white,  short  oval,  with  a  central 
brown  annulation,  and  is  spun  among  the  leaves  or  under  a  piece  of 
bark.  The  closely  allied  but  smaller  hemerobiid  larvae  also  attack 

walnut  plant  lice. 

SYRPHID  LARVAE. 

Next  to  the  ladybird  beetles  the  larvae  of  flies  of  the  family 
Syrphidae  are  of  greatest  importance  in  the  natural  control  of  walnut 
aphides.  The  author  has  reared  the  following  species  of  Syrphidae 
from  larvae  collected  while  they  were  feeding  on  walnut  aphides: 
Catabomba  pyrastri  Linnaeus  (1911-12) ;  Sph&rophoria,  melanosa  Wil- 
liston  (Aug.  24,  1912);  SpJiseropJioria  sulpJiuripes  Thomson  (Oct.  15, 
1911);  Allograpta  obliqua  S&y  (Aug.  6, 1912);  Eupeodes  volucris  Osten 
Sac  ken  (July,  1911).  SyrpJius  opinator  Osten  Sacken,  and  probably 
other  members  of  this  genus,  prey  on  the  aphides.  Catabomba  pyrastri 
is  the  most  abundant  as  well  as  the  largest  of  these  flies.  Its  aphido- 
phagous  capacity  is  almost  double  that  of  any  of  the  other  species 
enumerated  above.  Table  XI  indicates  the  predatory  activities  of 
two  larvae  of  the  last  brood  of  this  fly. 

TABLE  XI. — Catabomba  pyrastri:  Predatory  activities  on  walnut  plant  lice,  Santa  Jose, 

Cal.,  1912. 


Date. 

Number  of 
"lice"  eaten 
by- 

Date. 

Number  of 
"lice"  eaten 
by- 

Date. 

Number  of 
"lice  "eaten 
by- 

Larva 
No.  1. 

Larva 

No.  2. 

Larva 
No.  1. 

Larva 
No.  2. 

Larva 
No.  1. 

Larva 
No.  2. 

Aue  29 

0) 
4 

(') 

4 

Sept.9  
10 

53 
65 
76 
17 
70 
62 
84 
74 
71 

59 
85 
62 
20 
83 
77 
63 
83 
105 

Sept.  18 

92 
50 
36 
35 

2  14 

107 
104 
10 

213 

30"" 

P     19 

31  

15 
20 
12 
11 
11 
23 
68 

15 
15 
17 
17 
18 
36 
46 

11  

20  
21  
22 

Sept.  2  

4 

12  
13  
14 

Total  

5  
6  

15  
16  
17  

959 

1,035 

Hatched  on  this  date. 


1  Pupated  on  this  date. 


The  "lice"  consumed  were  of  a  similar  average  size  to  those  eaten 
by  the  chrysopid  larvae  (Table  X).  The  larva  of  Catabomba  pyrastri 
is  pale  green,  with  three  longitudinal  white  stripes  the  whole  length  of 
the  body,  and  when  fully  extended  exceeds  half  an  inch  in  length. 
The  anterior  segments  of  the  body  are  retractile,  giving  it  a  sluglike 
appearance.  If  food  is  plentiful  the  larva  moves  but  little,  although  it 
is  capable  of  rapid  crawling  over  the  foliage  if  food  is  scarce.  A  para- 
site, Bassus  sp.,  preys  upon  it,  often  destroying  as  much  as  two-thirds 

243747 


38 


BULLETIN   100,   U.    S.    DEPARTMENT  OF   AGRICULTURE. 


of  a  brood  and  thus  reducing  its  economic  value.  The  maggot  of  the 
fly  pupates  commonly  among  fallen  leaves  or  rubbish  at  the  base  of 
the  tree,  forming  a  light  brown  puparium  (sometimes  dark  purplish- 
brown,  in  which  case  the  specimen  is  parasitized),  with  a  paler 
median  longitudinal  stripe.  The  adult  fly  is  a  large,  shining  black 
form,  with  three  interrupted,  pale-yellow,  arcuate  cross-bands 
(rarely  wanting),  and  is  12  mm.  long.  Syrphid  larvae  may  be  found 
preying  upon  walnut  plant  lice  from  May  to  November,  although 
they  are  quite  scarce  in  the  two  extreme  months. 

LADYBIRD  BEETLES  (FAMILY  COCCINELLHXS:). 

Ladybird  beetles  are  the  principal  enemies  of  aphides  affecting 
walnuts.  The  author  has  observed  the  following  species  feeding  on 
these  aphides:  (1)  Olla  dbdominalis  Say;  (2)  Adalia  melanopleura 
Le  Conte;  (3)  Cocdnella  Juliana  Mulsant;  (4)  Adalia  Jiumeralis  Say; 
(5)  Hippodamia  convergent  Guerin;  (6)  Hippodamia  ambigua  Le 
Conte;  (7)  Cocdnella  calif ornica  Mannerheim;  (8)  Adalia  bipunctata 
Linnaeus;  (9)  CJiilocoms  orbus  Casey.  Nos.  1  to  8  in  both  adult 
and  larval  stages  feed  on  the  plant  lice  on  the  leaves,  while  the  adults 
of  the  Chilocorus  occasionally  attack  the  winter  eggs  on  the  limbs. 
Nos.  1  to  4  are  the  most  persistent  enemies  of  the  aphides,  the  others 
only  appearing  spasmodically  on  the  trees.  The  Hippodamia  group 
of  lady  birds  seems  to  prefer  such  intensely  gregarious  plant  lice  as 
the  plum  louse  (Hyalopterus  arundinis  Fabricius)  or  the  bean  aphis 
(Aphis  rumitis  Linnaeus)  and  pay  much  less  attention  to  the  more 
sporadic  varieties  such  as  the  aphides  on  walnuts. 

Table  XII  indicates  the  predatory  activities  of  five  larvae  of  Olla 
abdominalis  (the  ashy-gray  ladybird.) 

TABLE  XII. — Olla  abdominalis:  Predatory  activities  on  walnut  plant  lice,  San   Jose, 

Cal, 1912. 


Num- 

Num- 

Num- 

Larva 
No. 

Date  of 
hatching. 

Date  of 
molt  1  . 

ber  of 
"lice" 
eaten 
to  molt 

Date  of 
molt  2. 

ber  of 
"lice" 
eaten, 
molts  1 

Date  of 
molt  3. 

ber  of 
"lice" 
eaten, 
molts 

Date  of 
pupation  . 

Total 
"lice" 
eaten. 

Date  of 
adult 
emer- 

1. 

and  2. 

2  to  3. 

1 
2 

Aug.  27 

Aug.  30 
Sept.   5 

29 
38 

Sept.    2 
9 

36 
30 

Sept.    5 
12 

91 
45 

Sept.  13 
19 

477 
417 

Sept.22 

3 

31 

V      5 

24 

9 

33 

12 

50 

18 

237 

25 

4 

31 

5 

35 

9 

27 

12 

59 

18 

234 

25 

5 

31 

5 

39 

9 

31 

12 

53 

18 

320 

25 

In  all,  1,685  "lice"  were  eaten  in  90  days,  or  18.7  "lice"  per  day 
per  larva.  The  "lice "  were  of  similar  average  size  to  those  consumed 
by  the  lacewing  larvae  (Table  X).  It  was  noticed  that  before  the 
first  molt  the  ladybird  larvae  would  eat  only  very  small  aphides. 

The  following  is  a  brief  account  of  the  stages  of  the  ashy-gray  lady- 
bird (OUa  abdominalis')  (PL  III).  The  egg:  Yellow,  later  becoming 


WALNUT   APHIDES   IN    CALIFORNIA. 


39 


orange-colored;  cylindrical,  long  oval,  slightly  tapering  to  either  end, 
four  times  as  long  as  broad;  deposited  in  compact  masses  of  from  5  to 
25  on  the  leaf,  usually  on  the  underside,  and  with  their  long  axis  at 
right  angles  to  the  leaf  surf  ace ;  size,  1.3  by  0.35  mm.  The  larva:  All 
black  at  hatching,  later  with  pale  markings,  becoming  more  distinct 
after  each  successive  molt.  After  the  third  molt  the  general  color 
is  dark  purplish-black,  with  a  median  line  of  pale  brick-red  spots  on 
the  thorax  and  abdomen  and  also  two  lateral  rows  of  similar  spots. 
On  segments  1  and  4  of  the  abdomen  occur  also  two  pale  spots,  one  on 
either  side  of  the  median  brick-colored  spot  and  midway  between  it 
and  the  corresponding  lateral  spot.  The  full-grown  larva  has  a 
length  of  8  millimeters.  The  pupa:  General  color  white,  wing  pads 
sienna  brown.  A  large  number  of  black  spots  and  dashes  are  present 
but  the  prevailing  color  is  white.  Average  size,  4  by  3.3  mm.  The 
adult:  Hemispherical,  ashy-gray,  with  black  markings,  the  elytra 
sometimes  diffused  with  dull  reddish  blotches;  head  black,  with 
central  portion  white  or  light  gray;  thorax  (pronotum)  black,  with 
gray  margins;  elytra  ashy-gray,  with  eight  black  spots  on  each 
elytron;  legs  yellow;  abdomen  reddish-yellow;  average  size,  5.2  by 
4.2  mm.  The  adults  of  this  species,  If  confined  without  food,  will 
devour  one  another. 

Table  XIII  indicates  the  predatory  activities  of  two  larvae  of 
Adalia  melanopleura  on  walnut  plant  lice. 

TABLE  XIII. — Adalia  melanopleura:  Predatory  activities  on.  walnut  plant  lice,  Walnut 
Creek,  CaL,  1912. 


Num- 

Num- 

Num- 

Larva 

Date  of 

Date  of 

ber 
"lice" 

Date  of 

ber 

"lice" 

Date  of 

ber 
"lice" 

Date  of 

Total 

Date  of 
adult 

No. 

hatching. 

molt  1. 

eaten 

molt  2. 

eaten, 

molt  3. 

eaten, 

pupa- 

emer- 

to 

molts 

molts 

tion. 

gence. 

molt  1. 

Ito2. 

2  to  3. 

1 
2 

Sept.  17 

Sept.  20 
19 

41 

35 

Sept.  24 
22 

34 

Sept.  26 

30 
33 

Sept.  30 

181 

194 

Oct.  12 
12 

In  all,  375  plant  lice  were  eaten  in  26  days,  or  14.4  per  day  per  larva. 
The  feeding  period  of  both  larvae  was  13  days  as  contrasted  with  an 
average  of  practically  18  days  for  the  larvae  of  the  ashy-gray  lady- 
bird. Adalia  melanopleura  is  considerably  smaller  than  that  species, 
its  larva  consuming  in  a  period  of  13  days  half  as  many  plant  lice 
as  the  larva  of  the  larger  species  will  devour  in  18  days.  This 
larger  species  will  consume  70  larvae  in  a  single  day  while  the  maggot 
of  the  large  syrphid  fly  (Cataboniba  pyrastri)  will  dispose  of  over  100 
and  during  the  23  days  or  so  of  its  existence  will  devour  over  1,000,  or 
about  43.5  lice  per  day.  However,  in  contrasting  the  two  groups  of 
predaceous  insects— Syrphidse  and  Coccinellidae — it  must  be  remem- 
bered that  the  former  are  aphidophagous  only  in  the  larval  state 


40  BULLETIN   100,    U.    S.    DEPARTMENT   OF    AGRICULTURE. 

while  both  the  adults  and  larvae  of  ladybirds  feed  on  plant  lice. 
Mr.  E.  K.  Games,1  experimenting  in  the  State  Insectary  at  Sacra- 
mento, Cal.,  found  that  20  adult  beetles  of  Hippodamia  convergent 
averaged  21.8  aphides  per  day  and  that  the  larvae  of  this  species  oach 
consumed  from  250  to  300  plant  lice  during  their  larval  existence. 
He  found  that  adult  females  would  deposit  eggs  for  from  a  month  to 
six  weeks,  laying  on  the  average  15  eggs  per  day  and  feeding  on  the 
plant  lice  all  the  time.  Essig 2  states  that  in  the  walnut  orchards  of 
Ventura  County,  Cal.,  OTla  dbdominalis,  the  ashy-gray  ladybird,  is  by 
far  the  most  beneficial  insect  in  the  natural  control  of  the  European 
walnut  aphis  (ChromapTiis  juglandicola) . 

ARTIFICIAL  CONTROL  OF  WALNUT  APHIDES. 

The  writer  has  been  unable,  save  in  one  instance,3  to  find  any  pub- 
lished account  of  artificial  control  tried  or  adopted  for  walnut  plant- 
lice.  Until  the  year  1910  no  such  work  seems  to  have  been  performed 
along  this  line.4  In  August  of  that  year  Mr.  P.  R.  Jones,  late  of  the 
Bureau  of  Entomology,  carried  out  a  scries  of  laboratory  experiments 
with  a  view  to  determining  the  efficiency  of  various  washes  against 
these  aphides.  A  small  hand  pump  was  fitted  with  an  Eddy-chamber 
nozzle  and  the  applications  made  at  a  medium  high  pressure.  Care 
was  taken  that  not  enough  pressure  was  exerted  to  kill  any  of  the 
''lice"  by  the  force  of  the  spray  alone.  Examinations  were  made  10 
minutes  after -the  applications.  From  these  experiments  the  fol- 
lowing results  were  obtained: 

Commercial  tobacco  extract  No.  2,  containing  40  per  cent  nicotine,  at  strengths  of 
1-1,040  to  1-2,048,  effective;  dilutions  weaker  than  1-2,048,  not  effective. 

Commercial  tobacco  extract  No.  1  containing  about  4  per  cent  of  nicotine  at  strength 
of  1-60,  effective;  dilutions  weaker  than  1-60,  not  effective  (1-SO  partially  effective). 

Commercial  tobacco  extract  No.  1,  at  strengths  varying  from  1-60  to  1-200,  com- 
bined with  a  3  per  cent  distillate-oil  emulsion,  effective. 

Commercial  tobacco  extract  No.  2  at  strengths  varying  from  1-1,000  to  1-2,650  com- 
bined with  a  3  per  cent  distillate-oil  emulsion,  effective. 

Commercial  tobacco  extract  No.  1  at  strengths  "varying  from  1-60  to  1-200  combined 
with  a  2  per  cent  distillate-oil  emulsion,  effective. 

Commercial  tobacco  extract  No.  2  at  strengths  varying  from  1-1,000  to  1-2,620  com- 
bined with  a  2  per  cent  distillate-oil  emulsion,  effective. 

Distillate-oil  emulsion  at  2,  3,  and  4  per  cent  strengths,  effective. 

Commercial  lime-sulphur,  1-50,  combined  with  commercial  tobacco  extract  No.  1, 
1-100,  effective. 

»  Sept.,  1912.  Carnes,  E.  K.  Insectary  Division  Reports  for  the  months  of  June  and  July,  1912.  Mo. 
Bui.  Cal.  State  Hort.  Com.,  v.  1,  no.  10,  p.  820-82&. 

Some  experiments  with  the  common  ladybird  ( Hippodamia  convergent),  p.  821-826. 

»  Apr.,  1912.  Essig,  E.  O.  The  walnut  plant  louse  ( Chromaphis  juglandicola  [Kalt]  Walker).  Mo.  BuL 
Cal.  State  Com.  Hort.,  v.  1,  no.  5,  p.  190-194,  figs.  72-73. 

Control,?.  192. 

»  Cf.  Biennial  Crop  Pest  and  Hort.  Report  1911-1912,  Oregon  Agr.  Coll.  Exp.  Sta.  Jan.  10,  1913,  p.  165. 
"  Blackleaf  40  "  and  kerosene  emulsion  10  per  cent  recommended. 

*  Since  going  to  press  control  experiments  undertaken  in  the  spring  of  1913  In  Southern  California  by 
the  University  of  California  have  been  published  in  Circular  107  of  tne  Agricultural  Experiment  Station 
Of  the  University  of  California, 


Bui.  100,  U.  S.  Dept.  of  Agriculture. 


PLATE  III. 


THE  ASHY-GRAY  LADYBIRD  (,Ou_A  ABDOMINALIS). 
[A,  adult;  B,  eggs;  C,  larva;  D,  pupa.     (After  Essig.)] 


j|    100,  U.  S.  Dept   of  AgriculU 


PLATE  IV. 


FIG.  1  .—TREE  OF  THE  ROYAL  HYBRID  WALNUT  IN  GROVE  OF  MR.  F.  LEIB,  SAN  JOSE,  CAL. 


FIG.  2.— GENERAL  VIEW  OF  WALNUT  GROVE  OF  MR.  F.  LEIB,  SAN  JOSE,  CAL. 


WALNUT  APHIDES  IN   CALIFORNIA.  41 

Commercial  lime-sulphur,  1-50,  combined  with  commercial  tobacco  extract  No.  1, 
1-200,  effective. 

Commercial  lime  sulphur,  1-70,  combined  with  commercial  tobacco  extract  No.  2, 
1-1,000,  effective. 

Commercial  lime-sulphur  1^15,  combined  with  commercial  tobacco  extract  No.  2, 
1-2,000,  effective. 

It  is  noticeable  that  the  weaker  solutions  of  tobacco  extracts  were 
not  effective  alone,  but  when  combined  with  distillate-oil  emulsion  or 
lime-sulphur  proved  quite  satisfactory.  Possibly  the  most  success- 
ful result  was  obtained  with  distillate-oil  emulsion  of  only  2  per  cent. 
Field  experiments  failed,  however,  to  justify  the  use  of  this  wash  alone, 
for  it  proved  to  lack  the  killing  power  found  in  the  tobacco-extract 
sprays.  The  emulsion  serves,  however,  as  a  very  good  "spreader" 
for  the  nicotine  killing  agent,  since  it  serves  to  distribute  the  spray 
over  the  leaf  surface.  Commercial  tobacco  extract  No.  2  proved  to 
have  greater  insecticidal  value  than  commercial  tobacco  extract  No.  1, 
judging  by  the  corresponding  strengths  of  the  two  sprays;  and  there- 
fore in  the  field  only  the  former  was  used.  Foliage  tests  on  an  Eastern 
black  walnut  tree  were  made  of  all  the  washes  used  in  the  laboratory 
experiments,  and  in  no  case  was  any  burning  observed  to  result.  This 
type  of  walnut  seems  more  susceptible'  to  burning  injury  than  does 
the  European  or  so-called  "Persian"  walnut. 

FIELD  EXPERIMENTS. 

SPRING   AND   SUMMER  TREATMENT. 

Experiment  No.  1. — Lime-sulphur  (commercial  1-50)  combined  with  commercial 
tobacco  extract  No.  2  (1-1,500).  Orchard  of  Mr.  I.  Du  Bois,  San  Jose,  Cal.  Two  large 
European  walnut  trees  badly  infested  with  aphides  were  sprayed  July  1, 1911,  under  an 
even  pressure  of  170  pounds.  A  count  made  on  the  following  day  showed  that  95  per 
cent  of  the  aphides  had  been  destroyed  by  the  wash. 

Experiment  No.  2. — Three  per  cent  standard  distillate-oil  emulsion  combined  with 
commercial  tobacco  extract  No.  2  (1-2,000).  A  large,  badly  infested  European  walnut 
tree  in  the  yard  of  the  experiment  station  at  San  Jose  was  treated,  July  3,  1911,  with 
this  spray  at  an  even  pressure  of  170  pounds.  A  count  made  July  5  showed  that  over 
95  per  cent  of  the  aphides  had  been  killed. 

Experiment  No.  3. — Commercial  tobacco  extract  No.  2  (1-1,500).  Orchard  of  Mr. 
F.  Leib,  near  San  Jose,  Cal.  (PI.  IV,  figs.  1,  2).  A  block  of  10  walnut  trees  badly  infested 
was  sprayed,  May  21,  1912,  under  a  pressure  fluctuating  from  60  to  140  pounds.  A 
count  made  two  days  later  showed  that  not  over  40  per  cent  of  the  "lice"  were  de- 
stroyed. 

Experiment  No.  4- — Commercial  tobacco  extract  No.  2  (1-1,500)  combined  with  2 
per  cent  homemade  distillate-oil  emulsion.  Orchard  of  Mr.  F.  Leib,  near  San  Jose, 
Cal.  A  block  of  10  badly  infested  walnut  trees  was  sprayed,  May  21,  1912,  under 
pressure  similar  to  that  of  experiment  No.  3.  A  count  made  two  days  later  showed 
that  98  per  cent  of  the  insects  had  succumbed.  Some  oil  burning  appeared  on  the 
foliage  and  nuts  owing  to  insufficient  agitation  in  the  preparation  of  the  emulsion 
and  consequent  freeing  of  oil. 

Experiments  Nos.  3  and  4  were  made  to  determine  whether  the  tobacco  extract 
alone  would  prove  effective  in  the  field.  Results  indicate  that  a  weak  solution  of 
oil  emulsion  is  necessary  to  act  as  a  "spreader"  for  the  tobacco. 


42  BULLETIN   100,   U.    S.   DEPARTMENT  OF   AGEICULTUBE. 

Experiment  No.  5. — Distillate-oil  emulsion,  2  per  cent.  Orchard  of  Mr.  F.  Leib, 
near  San  Jose,  Cal.  A  block  of  six  badly  infested  walnut  trees  was  sprayed  under 
110  pounds  pressure,  July  31,  1912.  A  count  made  on  August  6  showed  that  74  per 
cent  of  the  "lice"  had  been  destroyed. 

Experiment  No.  6. — Distillate-oil  emulsion,  2  per  cent,  combined  with  commercial 
tobacco  extract  No.  2  (1-2,000).  Orchard  of  Mr.  F.  Leib,  near  San  Jose,  Cal.  (PL 
IV,  figs.  1,  2).  Six  walnut  trees,  badly  infested,  were  sprayed  under  a  pressure  of 
110  pounds.  A  count,  made  August  6,  showed  that  85  per  cent  of  the  "lice"  had 
been  killed  by  the  spray. 

Experiment  No.  7, — Whale-oil  soap,  1  pound;  water,  5  gallons.  Orchard  of  Mr. 
E.  I.  Hutchinson,  Concord,  Cal.  A  block  of  12  moderately  infested  European  walnut 
trees  was  sprayed  under  150  pounds  pressure,  May  10,  1913.  A  count  made  two  days 
later  showed  that  out  of  473  "lice"  counted,  263,  or  55.6  per  cent,  had  been  destroyed. 
A  thorough  drenching  had  been  applied  and  the  trees  were  in  full  leaf.  It  was  noticed 
that  the  great  majority  of  the  "lice"  that  escaped  were  situated  close  to  the  base  of 
the  midrib.  In  this  position  they  were  partly  protected  by  the  projecting  rib,  and 
it  is  to  be  supposed  that  the  wash  lacked  the  pressure  iiece-  nry  to  reach  these 
individuals. 

All  the  foregoing  experiments  were  undertaken  on  trees  on  which 
the  foliage  was  fully  developed.  It  was  noticeable  that  on  thickly 
foliated  trees  the  percentage  of  plant  lice  killed  was  the  smallest, 
while  on  thinly  foliated  trees  the  greatest  mortality  resulted.  Much 
of  the  leaf  surface  on  thickly  foliated  trees  is  almost  inaccessible 
to  spray. 

A  comparison  of  the  results  of  the  foregoing  tests  favors  distillate- 
oil  emulsion  and  tobacco.  The  most  desirable  combination  for  spring 
and  summer  spraying  is  a  2  per  cent  distillate-oil  emulsion,  commer- 
cial or  homemade,  combined  with  commercial  tobacco  extract  No. 
2,  1  to  1,500.  High  pressure  (150  pounds  or  over)  is  desirable, 
although  not  absolutely  necessary  unless  the  spraying  be  done  before 
the  walnut  leaflets  have  flattened  out  in  spring. 

In  tuning  the  application  for  the  aphides  on  the  leaves  it  is  desirable 
to  spray  as  early  as  possible  in  order  to  reduce  the  amount  of  leaf 
surface  to  be  covered  by  the  wash  and  to  destroy  the  plant  lice  before 
they  attack  the  nuts.  On  the  other  hand  it  will  be  found  very  hard 
to  destroy  the  plant  lice  before  the  leaflets  flatten  out,  for  the  young 
leaflets  are  pressed  against  one  another  in  a  manner  that  affords 
very  good  protection  to  the  insects  from  a  spray.  Moreover  at  this 
period  all  the  stem-mother  plant  lice  will  not  have  hatched  from 
the  winter  eggs.  The  time  most  preferable  for  the  application  is 
just  as  soon  as  the  growing  leaflets  shall  have  flattened  out  and  before 
they  have  attained  their  full  size.  At  this  time  the  "lice"  have  all 
hatched  and  are  all  exposed  on  the  underside  of  the  leaves.  Should 
an  oil  spray  be  applied  care  should  be  taken  that  there  is  no  free  oil 
in  the  emulsion,  as  the  young  nuts  are  susceptible  to  burning.  No 
stronger  than  a  2  per  cent  distillate-oil  emulsion  should  be  used  for 
this  early  application.  The  spray  should  be  directed  to  the  underside 
of  the  leaves,  and  angle  nozzles  used.  A  round  nozzle  is  to  be  pre- 


WALNUT  APHIDES  IN   CALIFORNIA. 


ferred  to  one  of  the  Clipper  type,  as  the  former  will  diffuse  the  spray 
better  over  the  leaf  surface.  Such  a  driving-spray  nozzle  as  that 
devised  by  the  Massachusetts  Agricultural  College  is  desirable  for 
spraying  trees  of  large  size.  If  there  are  unsprayed  walnut  trees 
in  the  vicinity  it  may  be  necessary  to  make  a  second  application 
some  two  or  three  weeks  later,  as  plant  lice  are  apt  to  have  migrated 
from  these  to  the  sprayed  trees. 

On  account  of  the  extended  period  over  which  the  sexual  forms  are 
produced,  fall  spraying  for  these  forms,  unless  repeated  again  and 
again,  will  be  of  little  value. 

It  should  be  borne  in  mind  that  the  number  of  "lice"  hatching  in 
the  spring  from  the  winter  eggs  varies  considerably  year  by  year  in  a 
given  locality  or  orchard  and  also  that  the  hatching  time  of  these 
"lice"  is  regulated  by  the  sap  flow  in  that  particular  tree  upon  which 
the  eggs  happened  to  be  placed.  The  hatching  of  the  winter  eggs 
is  not  regulated  by  temperature  conditions.  Hence  the  stage  in  the 
seasonal  development  of  the  aphidids  corresponds  to  the  stage  in 
development  of  that  particular  tree  on  which  the  stem-mother  lice 
were  produced,  leaving  out  of  consideration  the  possibility  of  mi- 
grants arriving  from  other  trees.  This  point  is  of  importance  when 
it  is  considered  that  the  different  varieties  of  cultivated  walnuts  put 
out  their  leaves  and  produce  their  nuts  at  different  times  and  that 
these  functions  are  performed  by  individual  varieties  at  different 
times  dependent  on  locality  and  seasonal  meteorological  conditions. 

Table  XIV  summarizes  the  control  experiments  made  for  spring 
and  summer  treatment. 


TABLE  XIV.  —  Summary  of  spring  and  summer  spraying  experiments  against  walnut 
aphides,  San  Jose  and  Walnut  Creek,  Cal.,  1911,  1912,  and  1913. 

Result  of 

Character  of  spray. 

Date  of  appli- 
cation. 

Number 

trees 
sprayed. 

spray;  per 
cent  of 
plant  lice 
killed. 

Cost  per 
diluted 
gallon. 

Commercial  lime-sulphur,  1-50  and  commercial  tobacco 

extract  No  2(11  500) 

July     1,1911 

95 

$0.012 

3  per  cent  distillate-oil  emulsion  (homemade)  and  com- 
mercial tobacco  extract  No.  2  (1-2,000)  

July     3,1911 

t 

95 

.0088 

Commercial  tobacco  extract  No.  2  (1-1,500)  
2  per  cent  distillate-oil  emulsion  (homemade)  and  com- 

May   21,1912 
do 

10 
10 

40 
98 

.008 
.0098 

2  per  cent  distillate-oil  emulsion  (commercial)  
2  per  cent  distillate-oil  emulsion  (commercial)  and  com- 
mercial tobacco  extract  No.  2  (1-2,000)  

July   31,1912 
....do  

6 
6 

74 

85 

.0067 
.0127 

Whale-oil  soap  (homemade),  1  pound  to  5  gallons  water.. 

May   10,1913 

12 

55.6 

.004 

WINTER   TREATMENT. 

Experiment  No.  1.— Crude-oil  emulsion,  12  per  cent  (crude  oil,  27  °Baume').  Orchard 
of  Mr.  George  Whitman,  Concord,  Cal.  A  block  of  31  European  walnut  trees  of  moder- 
ate size  were  sprayed  February  25,  1913,  under  a  pressure  of  from  150  to  175  pounds. 
Three  gallonsof  spray  were  applied  to  each  tree  and  "Friend"  nozzles  used.  The  trees 
were  well  drenched.  Examination  made  April  5,  1913,  showed  that  trees  were  start- 
ing to  leaf.  Most  of  the  leaves  were  as  yet  tightly  closed,  but  the  basal  leaves  of  many 


44  BULLETIN   100,   U.    S.    DEPARTMENT  OP   AGRICULTURE. 

shoots  were  opened.  A  general  survey  of  the  sprayed  block  and  of  a  check  unsprayed 
block  indicated  equal  infestation  by  young  stem  mothers.  Plant  lice  were  not  all 
hatched.  An  examination  made  April  15,  1913,  showed  that  trees  were  well  out  in 
leaf.  All  stem  mothers  had  hatched .  A  general  survey  of  sprayed  and  unsprayed 
trees  showed  no  apparent  difference  in  infestation.  A  count  of  28  leaf  clusters  selected 
at  random  from  the  sprayed  trees  yielded  21  stem  mothers,  while  a  similar  count  of 
the  same  number  of  leaf  clusters  from  unsprayed  trees  yielded  29  stem  mothers.  It 
may  be  inferred  from  this  experiment  that  the  crude-oil  emulsion  destroyed  few,  if 
any,  of  the  winter  eggs. 

Experiment  No.  2. — Commercial  lime-sulphur,  1-10.  (Concentrated  solution,  33° 
Baum6.)  Orchard  of  Mr.  George  Whitman,  Concord,  Cal.  A  block  of  four  large  trees 
of  the  European  walnut  were  sprayed  March  5,  1913,  under  a  pressure  of  100  pounds. 
About  14  gallons  of  spray  were  applied  to  each  tree  and  "  Friend"  angle  nozzles  used. 
Eggs  were  abundant  on  both  sprayed  and  check  trees.  The  leaf  buds  on  these  trees 
began  to  open  April  1, 1913.  Examination  was  made  April  15, 1913.  Trees  were  then 
well  out  in  leaf.  The  stem  mothers  were  all  hatched.  The  lime  had  no  effect  in 
retarding  leafing.  A  count  of  20  leaf  clusters  taken  at  random  on  the  sprayed  block 
yielded  no  plant  lice,  while  a  similar  count  of  the  same  number  of  leaves  on  the  check 
trees  yielded  27  stem  mothers.  Further  examination  showed  that  on  the  sprayed 
trees  no  plant  lice  could  be  found,  while  on  the  check  trees  nearly  every  leaf  cluster 
had  one  or  more  of  the  insects. 

A  subsidiary  experiment  was  undertaken  on  two  young  California  black  walnut 
trees,  both  infested  with  eggs.  One  of  these  trees  was  treated  with  commercial  lime- 
sulphur,  1-9  (concentrated  solution  33°  Baum6),  and  the  other  left  as  a  check.  On 
the  sprayed  tree  no  eggs  hatched  and  when  examined  on  April  17,  1913,  the  eggs  were 
shrunken  and  distorted,  the  embryos  having  been  destroyed  within  the  eggshell. 
The  eggs  on  the  check  tree  hatched  normally  about  the  end  of  March. 

Experiment  No.  S. — Crude-oil  emulsion,  lime-sulphur,  and  "Yel- 
ros."  Vrooman  orchard,  Santa  Rosa,  Cal.  Four  plats  were 
sprayed,  April  9-11,  1913,  with  a  power  outfit  at  high  pressure,  as 
follows:  Plat  1,  40  trees,  crude  oil  (22°  Baume")  emulsion,  8  per  cent; 
plat  2,  40  trees,  lime-sulphur,  1  to  8;  plat  3,  "Yel-ros,"  1  to  25, 
16  trees;  plat  4,  "Yel-ros,"  1  to  40,  24  trees.  These  applications 
were  made  on  late  Franquette  walnuts,  dormant  at  the  time  of  spray- 
ing. The  orchard  was  well  infested  with  the  winter  eggs  of  the  plant 
lice.  An  examination,  May  27,  1913,  showed  that  the  trees  were  well 
out  in  leaf.  Stem  mother  plant  lice  were  mostly  about  two-thirds 
grown.  Counts  of  80  leaves  (about  480  leaflets)  taken  at  random 
from  each  of  the  four  plats  and  from  a  check  unsprayed  plat  resulted 
as  follows: 


TABLE  XV. — Winter  spraying  experiment   No.   S  against  walnut  aphides, 
orchard,  Santa  Rosa,  Cal.,  1913. 


Vrooman 


Number  of 

Percent 

Plat. 

"lice"  on 

of  number 

80  leaves. 

on  check. 

Crude-oil  emulsion,  8  per  cent  

11 

10.6 

Lime-sulphur.  1  to  8.                                                               

2 

1.9 

"  Yel-ros  "  1  to  25                                                                                            

14 

13.4 

"Yel-ros  "  1  to  40 

97 

93  2 

Check  —  unsprayed  .         ...             

104 

100.0 

WALNUT  APHIDES  IN   CALIFORNIA. 


45 


The  best  results,  therefore,  were  obtained  by  the  lime-sulphur 
wash.  The  greater  efficiency  of  the  8  per  cent  crude-oil  emulsion 
over  the  12  per  cent  crude  oil  used  in  experiment  No.  1  is  probably 
due  to  the  heavier  grade  of  oil  (22°  Baume")  used  in  the  8  per  cent 
experiment.  The  heavier  oil  remains  longer  on  the  trees  and  coats 
the  eggs  of  the  aphides  more  satisfactorily  than  the  oil  of  lighter 
grade.  As  may  be  seen  from  Table  XVI  both  the  8  per  cent  crude- 
oil  emulsion  and  "  Yel-ros,"  1  to  25,  gave  good  results,  but  "  Yel-ros," 
1  to  40,  was  quite  ineffective.  Table  XVI  is  a  summary  of  experiments 
against  the  winter  eggs: 

TABLE  XVI. — Summary  of  experiments  on  the  winter  eggs,   Walnut  Creek  and  Santa 
Rosa,  Cal,  1913. 


Plant 

Character  of  spray. 

Date  of  ap- 
plication. 

Number 
of  trees 
sprayed. 

Date  of  ex- 
amination. 

lice 
present 
(check— 

Cost  per 
diluted 
gallon. 

100). 

Per  cent. 

Crude-oil  (27°  Baume1)  emulsion,  12  per  cent  

Feb.  25.... 
Mar  5 

31 
4 

Apr.  5,  15.  . 
do 

72.4 
0 

J0.01 
02 

Crude-oil  (22°  Baum6)  emulsion,  8  per  cent  
Commercial  lime-sulphur,  1  to  8  

Apr.  9-11.. 
do  

40 
40 

May  27.... 
do  

10.6 
1.9 

.0073 
.025- 

"Yel-ros  "  1  to  25 

do 

16 

do 

13  4 

028 

"Yel-ros,"  1  to  40    .  .             

do.... 

24 

do.... 

93.2 

.0175 

It  is  in  a  measure  unfortunate  that  the  homemade  1-2-1  lime- 
sulphur  spray  was  not  tried.  This  is  considerably  cheaper  than  the 
commercial  article,  but  there  is  no  reason  to  suppose  that  the  winter 
formula  of  the  homemade  lime-sulphur  would  not  prove  quite  effective 
judging  by  the  results  obtained  with  commercial  lime-sulphur. 

In  recommending  winter  sprays  for  the  plant  lice  infesting  walnut 
trees  the  writer  must  accord  the  preference  to  lime-sulphur,  1-8  to 
1-11,  while  good  work  may  be  expected  from  crude-oil  emulsion,  8  to 
12  per  cent,  using  the  heavier  grades  of  oil  (not  lighter  than  24° 
Baume),  and  from  "  Yel-ros,"  1-25.  The  oil  emulsion  (homemade)  is 
the  cheapest  winter  spray,  although  there  is  li ttle  difference  between  its 
cost  and  that  of  the  homemade  lime-sulphur  wash,  winter  formula. 

In  applying  the  spray  for  the  aphis  eggs  the  wash  should  be  directed 
so  as  to  cover  completely  every  part  of  the  twigs  and  limbs.  Late 
spraying,  i.  e.,  making  the  application  just  before  the  buds  are  begin- 
ning to  swell,  is  preferable  to  spraying  earlier,  especially  if  crude-oil 
emulsion  is  used,  as  the  oil  does  its  best  work  soon  after  it  is  applied 
and  the  plant  lice  at  hatching  time  are  more  easily  destroyed  by  it. 

In  concluding  the  section  on  artificial  control  the  author  would  like 
to  express  his  thanks  to  Mr.  Frank  Leib,  San  Jose,  Cal.,  and  Messrs. 
George  Whitman  and  E.  I.  Hutchinson,  Concord,  Cal.,  for  their  help  and 
cooperation  in  the  carrying  out  of  field  experiments  on  their  orchards, 
and  also  to  Balfour,  Guthrie  &  Co.,  San  Francisco,  Cal.,  by  whose 
courtesy  the  Santa  Rosa  experiments  were  made  possible,  they  having 
made  the  spray  applications  under  the  author's  supervision. 


46  BULLETIN   100,   U.    S.    DEPARTMENT  OF   AGRICULTURE. 

SUMMARY. 

The  life  history  of  walnut  aphides  in  California  is  briefly  as  follows: 
A  week  or  so  before  the  buds  open  on  the  trees  in  the  spring  the 
aphiclids  begin  to  hatch  from  the  winter  eggs.  As  soon  as  the  young 
foliage  appears  the  "lice"  settle  on  it,  and  after  feeding  for  a  month 
or  so  become  adults.  These  stem  mothers  are  always  winged  and  like 
plant  lice  of  later  generations  are  capable  of  migrating  to  other  trees 
and  orchards.  As  soon  as  they  are  fully  developed  they  produce 
young  parthenogenetically.  These  second-generation  young  become 
mature  in  three  weeks  and  in  turn  produce  young.  The  individuals 
of  the  third  and  subsequent  generations  of  summer  mature  in  about 
16  days.  On  early-leafing  varieties  there  are  10  or  11  viviparous 
generations  in  the  year  while  on  late  varieties  there  are  8  or  9.  The 
production  of  the  sexual  generation  is  prolonged  over  four  months, 
these  forms  first  appearing  in  July.  After  the  sexes  (comprised  of 
the  winged  male  and  the  wingless  female)  mate,  the  female  repairs  to 
the  twigs  and  limbs  of  the  tree,  there  to  deposit  her  eggs.  Winter  is 
passed  in  the  egg  stage  only. 

In  general  the  aphidids  inhabit  the  underside  of  the  leaves,  but  those 
of  the  second,  third,  and  fourth  generations  often  attack  the  nuts, 
sometimes  seriously  dwarfing  them  (see  PI.  I,  fig.  1).  Occasionally 
the  "lice"  will  be  found  on  the  upper  surface  of  the  leaf.  When  infes- 
tation on  the  leaves  and  nuts  is  severe  the  vitality  of  the  infested  tree 
is  impaired.  The  aphidids  excrete  a  sweet,  gummy,  transparent  sub- 
stance much  sought  after  by  ants,  and  in  this  thrives  a  black  sooty 
fungus.  This  black  fungus  often  covers  the  upper  sides  of  the  lower 
leaves  and  the  upper  part  of  the  nuts,  thereby  interfering  with  the 
respiratory  action  of  the  plant  tissues. 

Walnut  plant  lice  have  many  natural  foes,  all  predatory.  These 
serve  to  keep  the  aphidids  in  check  but  do  not  appear  in  sufficient 
numbers  until  after  the  "lice"  have  had  time  to  injure  the  nuts.  The 
most  persistent  of  them  is  the  ashy-gray  ladybird  beetle  (Olla  abdom- 
indLis  Say). 

Aphidids  on  walnuts  can  be  controlled  artificially  with  sprays.  The 
winter  spraying  directed  against  the  eggs  is  the  easier  to  apply,  and  high 
trees  can  be  reached  by  a  winter  wash  with  ease,  whereas  in  the  spring 
and  summer  so  thick  is  the  foliage  that  a  thorough  application  is  hard 
to  accomplish  satisfactorily.  Furthermore,  far  less  material  is 
required  when  the  trees  are  bare.  Lime-sulphur  and  crude-oil  emul- 
sions are  effective,  especially  the  first  named.  The  spray  should  be 
directed  all  over  limbs  and  twigs  so  as  to  cover  every  part.  If  it 
is  necessary  to  spray  in  spring  or  summer,  a  combination  of  2  per  cent 
distillate-oil  emulsion  and  commercial  tobacco  extract  No.  2  (1  to 
1,500)  will  prove  effective  provided  it  be  applied  under  a  pressure  of 
at  least  150  pounds  and  the  spray  directed  on  the  nuts  and  underside 
of  the  leaves. 


WALNUT   APHIDES   IN    CALIFORNIA.  47 

BIBLIOGRAPHY. 

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1843.  Kaltenbach,  J.  H.  Monographic  der  Familieii  der  Pflanzenlause  .  .  .  Aachen, 
1843. 

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"  Callipterus  juglandicola  Kalt."  recorded. 

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1910.  Wilson,  H.  F.  A  key  to  the  genera  and  notes  on  the  synonymy  of  the  tribe 
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1912. 

Description  and  figures,  natural  control  notes. 

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"  Callipterus  caryse,  n.  sp.,"  p.  31.    Original  description. 

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48  BULLETIN   100,   U.    S.   DEPARTMENT  OF   AGRICULTURE. 

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